Micro-channel-cooled high heat load light emitting device

ABSTRACT

Micro-channel-cooled UV curing systems and components thereof are provided. According to one embodiment, a lamp head module includes a high aspect ratio, high fill factor array of light emitting devices and a submount. The array includes multiple groups of electrically seriesed light emitting devices that are connected in electrical parallel. The submount is of monolithic construction and includes multiple L-shaped patterned circuit material layers. Each of the L-shaped patterned circuit material layers includes an arm portion and a stem portion. The arm portion functions as a light emitting device bond pad and the stem portion functions as a wire bond pad and a circuit trace. Each light emitting device of a group is affixed to a corresponding arm portion of the submount. The stem portions are located external to the array, run parallel to the length of the array and perform a primary current carrying function for current flow between adjacent light emitting devices of the group.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/589,519 filed on Aug. 20, 2012, which is a continuation-in-part ofU.S. patent application Ser. No. 13/014,069 filed on Jan. 26, 2011, nowU.S. Pat. No. 8,378,322, which claims the benefit of priority to U.S.Provisional Patent Application No. 61/336,979, filed on Jan. 27, 2010;U.S. Provisional Patent Application No. 61/341,594, filed on Apr. 1,2010; and U.S. Provisional Patent Application No. 61/456,426, filed onNov. 5, 2010, all of which are hereby incorporated by reference in theirentirety for all purposes.

COPYRIGHT NOTICE

Contained herein is material that is subject to copyright protection.The copyright owner has no objection to the facsimile reproduction ofthe patent disclosure by any person as it appears in the Patent andTrademark Office patent files or records, but otherwise reserves allrights to the copyright whatsoever. Copyright© 2010-2014, HeraeusNoblelight Fusion UV Inc.

BACKGROUND

Field

Embodiments of the present invention generally relate tomicro-channel-cooled light emitting diodes (LEDs). In particular,embodiments of the present invention relate to high power density, highfill-factor, micro-channel-cooled ultraviolet (UV) LED lamp head modulesthat provide high brightness, high irradiance and high energy density.

Description of the Related Art

Today's UV LEDs remain relatively inefficient (typically, operating atabout 20% efficiency when operated at high current densities). Theseinefficiencies result in the production of large quantities of wasteheat and therefore require at least air cooling and often liquid cooling(e.g., heat exchangers and/or chillers) to remove the unwanted wasteheat, which is a by-product of the electrical to optical conversionprocess within the p-n junction of the semiconductor device. If the heatis not removed in a very effective and efficient manner, the LED devicesmay suffer loss of efficiency, decrease in light output and evencatastrophic failure.

Liquid-cooled UV LED lamps (or light engines) are currently being usedin a variety of curing applications; however, existing systems haveseveral limitations. For example, while industry literature acknowledgesthe desirability of high brightness/high irradiance arrays, currentlyavailable UV LED lamps provide sub-optimal performance.

A specific example of a prior art UV LED array is illustrated in FIGS.1A and 1B. In this example, which is taken from US Pub. No 2010/0052002(hereafter “Owen”), an alleged “dense” LED array 100 is depicted forapplications purported to require “high optical power density”. Thearray 100 is constructed by forming micro-reflectors 154 within asubstrate 152 and mounting an LED 156 within each micro-reflector 154.The LEDs 156 are electrically connected to a power source (not shown)through a lead line 158 to a wire bond pad on substrate 152. Themicro-reflectors 154 each include a reflective layer 162 to reflectlight produced by the associated LED 156. Notably, despite beingcharacterized as a “dense” LED array, LED array 100 is in reality a verylow fill-factor, low brightness, low heat flux array in that theindividual LEDs 156 are spaced quite some distance apart having acenter-to-center spacing of about 800 microns. At best, it would appearthe LEDs account for approximately between 10 to 20% of the surface areaof LED array 100 and certainly less than 50%. Such low fill-factor LEDarrays can create an uneven irradiance pattern that can lead to unevencuring and visually perceptible anomalies, such as aliasing andpixelation. Additionally, the micro-reflectors 154 fail to capture andcontrol a substantial amount of light by virtue of their low angularextent. Consequently, array 100 produces a low irradiance beam thatrapidly loses irradiance as a function of the distance from thereflector 154. It is to be further noted that even optimally configuredreflectors would not make up for the low brightness of LED array 100 asthe ultimate projected light beam onto the work piece can never bebrighter than the source (in this case LED array 100). This is due tothe well-known conservation of brightness theorem. Furthermore, Owenalso teaches away from the use of macro-reflectors due to their size andthe perceived need to have a reflector associated with each individualLED 156.

The aforementioned limitations aside, the relatively large channelliquid cooling technology employed in prior-art cooling designs is notcapable of removing waste heat from the LEDs in a manner that would beeffective in keeping junction temperatures adequately low when thecurrent per square millimeter exceeds approximately 1.5 amps.

Oxygen inhibition is the competition between ambient oxygen reactingwith the cured material at a comparable rate as the chemicalcross-linking induced by the UV light and photoinitiator (PhI)interaction. Higher irradiance is known to create thorough cures morerapidly and higher irradiance is known to at least partially addressoxygen inhibition issues. Ultra high irradiance is now thought toperhaps overcome oxygen inhibition issues in certain processconfigurations perhaps even without a nitrogen cover gas. However, toproduce ultra high irradiance to overcome oxygen inhibition, the heatflux removal rate needed to keep junction temperatures adequately low insuch a high fill-factor LED array environment operating at extremelyhigh current densities and is simply not attainable with currentlyemployed UV LED array architectures and UV LED array coolingtechnologies.

SUMMARY

Micro-channel-cooled UV curing systems and components thereof aredescribed that are configured for photo-chemical curing of materials andother high-brightness applications. According to one embodiment a lamphead module is provided with an array of light emitting devices (LEDs)and a submount. The array has a high aspect ratio in which a length ofthe array is greater than a width of the array. The LEDs are closelyspaced to create a high fill factor. The array includes multiple groupsof electrically seriesed LEDs that are connected in electrical parallel.The submount is of monolithic construction and includes multipleL-shaped patterned circuit material layers. Each of the L-shapedpatterned circuit material layers includes an arm portion and a stemportion. The arm portion functions as an LED bond pad and the stemportion functions as both a wire bond pad and a circuit trace. Each LEDof a group of electrically seriesed LEDs is affixed to a correspondingarm portion of the submount. The stem portions are located substantiallyexternal to an area defined by the length and width of the array, runsubstantially parallel to the length of the array and collectivelyperform a primary current carrying function for current flow betweenadjacent LEDs of a group of electrically seriesed LEDs.

In another embodiment, a lamp head module includes an array of lightemitting devices (LEDs) and a pair of optical macro-reflectors. Thearray has a high aspect ratio in which a length of the array is greaterthan a width of the array. The pair of optical macro-reflectors directphotons emitted by the array and produce a beam pattern having a top hatprofile on a surface of a workpiece.

In yet another embodiment, a lamp head module includes a lamp body, apower source, a high brightness and high aspect ratio array of lightemitting devices (LEDs), a submount and a flex circuit. The power sourceincludes an anode output connection and a cathode output connection. Thearray has a light emitting surface. The submount is configured toelectrically couple a multiple LEDs of the array in electrical seriesand includes multiple LED bond pad areas and multiple wire bond areas.The flex circuit is mounted to the lamp body and has a high aspect ratioin terms of its length and height. The flex-circuit has formed therein alocating aperture within which the submount is mounted and includesopposite electrical polarity conductive patterned layers including ananode layer and a cathode layer. A first end of the flex-circuit exposesa first portion of the anode layer to form an electrical connection withthe anode output connection of the power source and exposes a firstportion of the cathode layer to form an electrical connection with thecathode output connection of the power source. A second end of theflex-circuit exposes a second portion of the anode layer, which iselectrically coupled to an LED bond pad area associated with a first LEDof a group of electrically seriesed LEDs. The second end of theflex-circuit exposes a second portion of the cathode layer, which iselectrically coupled to a cathode portion of a wire bond area that isassociated with a last LED of the group.

Other features of embodiments of the present invention will be apparentfrom the accompanying drawings and from the detailed description thatfollows.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are illustrated by way of example,and not by way of limitation, in the figures of the accompanyingdrawings and in which like reference numerals refer to similar elementsand in which:

FIG. 1A is a top view of a portion of a prior art LED array.

FIG. 1B is a view of the LED array of FIG. 1A taken along section line1B-1B.

FIG. 2A is an isometric view of a UV LED lamp head module in accordancewith an embodiment of the present invention.

FIG. 2B is a front view of the UV LED lamp head module of FIG. 2A.

FIG. 2C is a side view of the UV LED lamp head module of FIG. 2A.

FIG. 3A is a top-level isometric cut-away view of the UV LED lamp headmodule of FIG. 2A.

FIG. 3B is a top-level front cut-away view of the UV LED lamp headmodule of FIG. 2A.

FIG. 4A is a magnified isometric cut-away view of a bottom portion of areflector and a top portion of a body of the UV LED lamp head module ofFIG. 2A.

FIG. 4B is a magnified front cut-away view of a bottom portion of areflector and a top portion of a body of the UV LED lamp head module ofFIG. 2A.

FIG. 5A is a further magnified isometric cut-away view illustrating anLED array and its interface with a common anode substrate layer of theUV LED lamp head module of FIG. 2A.

FIG. 5B is a further magnified front cut-away view illustrating an LEDarray and its interface with a common anode substrate layer of the UVLED lamp head module of FIG. 2A.

FIG. 6 is an exploded magnified isometric cut-away view of a top portionof a body of and illustrating various layers of the UV LED lamp headmodule of FIG. 2A.

FIG. 7 is a magnified isometric view of a reflector of the UV LED lamphead module of FIG. 2A with the end cap removed.

FIG. 8A conceptually illustrates two macro-reflectors of substantiallythe same height for different working distances in accordance with anembodiment of the present invention.

FIG. 8B is a magnified view of FIG. 8A illustrating marginal rays for a2 mm macro-reflector in accordance with an embodiment of the presentinvention.

FIG. 9 shows a macro-reflector optimized for a 2 mm focal plane in whicheach side of the reflector has a focal point that is offset from thecenterline of the focused beam on the work piece in accordance with anembodiment of the present invention.

FIG. 10 is a graph illustrating estimated convective thermal resistancefor various channel widths.

FIG. 11 is a graph illustrating output power for various junctiontemperatures.

FIG. 12 is a graph illustrating an irradiance profile for a UV LED lamphead with a reflector optimized for a 2 mm focal plane in accordancewith an embodiment of the present invention.

FIG. 13 is a graph illustrating an irradiance profile for a UV LED lamphead with a reflector optimized for a 53 mm focal plane in accordancewith an embodiment of the present invention.

FIG. 14A is an isometric view of a UV LED lamp head module in accordancewith an alternative embodiment of the present invention.

FIG. 14B is a side-facing, exploded view of the UV LED lamp head moduleof FIG. 14A.

FIG. 14C is a rear-facing, exploded isometric view of the UV LED lamphead module of FIG. 14A.

FIG. 14D is an exploded view of a flex circuit subsystem and coolingsubsystem in accordance with an embodiment of the present invention.

FIG. 15A is a top view of a submount in accordance with an embodiment ofthe present invention.

FIG. 15B is an isometric view of the submount of FIG. 15A.

FIG. 15C is a cross section of the submount of FIG. 15A.

FIG. 15D is an enlarged view of section D of FIG. 15A.

FIG. 16A is a top view of the flex circuit of FIG. 14B.

FIG. 16B is an isometric exploded view of the flex circuit of FIG. 14B.

FIG. 16C is a magnified front cut-away view illustrating an LED arrayand its interface with a submount and various flex circuit layers inaccordance with an embodiment of the present invention.

FIG. 17A is an isometric view of the LED array assembled to the flexcircuit and the micro-channel cooler in accordance with an embodiment ofthe present invention.

FIG. 17B is a top view of the LED array of FIG. 17A.

FIG. 17C is an enlarged view of section A of FIG. 17A showing wire-bondconnections for a group of electrically seriesed LEDs of the LED arrayof FIG. 17B.

FIG. 17D is a further enlarged view of section AA of FIG. 17B showing afirst LED of the group of electrically seriesed LEDs.

FIG. 17E is a further enlarged view of section AB of FIG. 17B.

FIG. 17F is a further enlarged view of section AC of FIG. 17B.

FIG. 18A conceptually illustrates a power path of a group ofelectrically seriesed LEDs in accordance with an embodiment of thepresent invention.

FIG. 18B is a magnified view of the first 4 LEDs of the group ofelectrically seriesed LEDs of FIG. 18A.

FIG. 18C is a cross section of the group of electrically seriesed LEDsof FIG. 18A taken along section line A.

FIG. 18D conceptually illustrates a power path of a group ofelectrically seriesed LEDs in accordance with an embodiment of thepresent invention.

FIG. 19 illustrates irradiance patterns from an 80 mm long reflectorthat creates a 25 mm wide irradiated area focused 65 mm below thereflector opening in accordance with an embodiment of the presentinvention.

FIG. 20 is a graph illustrating cross sections of various irradianceprofiles at a center of a workpiece surface for 5 mm, 25 mm and 50 mmstand-off distances in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION

Micro-channel-cooled UV curing systems and components thereof aredescribed that are configured for photo-chemical curing of materials andother applications requiring high fill-factor, high current density andhigh-brightness attributes (which ultimately leads to the attribute ofhigh-irradiance). According to one embodiment of the present invention,LEDs of a high fill factor LED array of an ultra high irradiance UVcuring system are placed in series/parallel with one or more groups ofLEDs in series run by a corresponding power source. For example,multiple groups of LEDs in series can be run by a single power source,each group can be run by its own power source or a combination thereof.UV curing systems can provide a wide range of wave lengths from 100nanometers to 10,000 nanometers.

According to embodiments of the present invention, in order toaccommodate the heat flux/thermal demands of a high fill-factor, highcurrent density and high-brightness UV LED lamp head module, practicalmeans to achieve isothermal substrate behavior are also provided.According to one embodiment, an LED array is directly bonded to amicro-channel cooler and the coolant flows across and underneath the LEDarray in a direction substantially parallel to the shortest dimension ofthe LED array. In one embodiment, coolant flow through micro-channelsrunning beneath the LEDs is approximately equal (e.g., balanced) so thatthe p-n junctions of the LEDs of the LED array are substantiallyisothermal. In one embodiment, the high aspect ratio substrate issubstantially isothermal from side to side and end to end. This may beachieved through the use of a substantially copper micro-channel coolerhaving micro-channels that direct the coolant flow under the LED arrayin a substantially lateral direction to the longitudinal axis of the LEDarray, while maintaining a tight flow balance range between eachchannel. In one embodiment, this flow balance is achieved by designingthe primary coolant inlet and exit coolant fluid channels that runparallel to the longitudinal axis of the LED array to reach a level ofpressure drop that is nearly homogeneous along their length.

In various embodiments, a multi-layer flex-circuit, bonded to amicro-channel cooler, is used to power groups of LEDs of an LED array soas to allow a pair of macro-non-imaging-optical reflectors to bepositioned in close proximity to the LED array, which thereby maintainsirradiance by maximizing the number of emitted photons that arecontrolled by the reflector pair.

In some embodiments, the LED array is driven by an AC/DC power supply(sometimes referred to as a rectifier) available from General Electric(GE) of Niskayuna, N.Y. and preferably has a high voltage swing, whereasthe typical 48V DC output has a range of 1% or so. For example, in oneembodiment, a power supply having a voltage swing of approximately +/−20to 25% while still maintaining high efficiency (e.g., approximately 97%or more), compactness and low cost is used. GE-Lineage of Plano, Tex.,makes a range of 12, 24 and 48V AC-DC power supplies that are high MTBFand highly efficient and are intended primarily for the data storage andtelecommunications industries. Embodiments of the present inventionadvantageously employ a preferably 48V “large voltage swing” model,e.g., the CP2000, that can efficiently output a range of user selectedoutput voltages below and above the nominal 48V. Most power supplies donot have this large voltage swing feature—especially OTS, efficient, andcost effective. The voltage can be user selected through a +/−5V input.This voltage swing ultimately allows for easy control of the opticalpower emitted by the LED array.

In some embodiments, factory and/or field replaceable macro-reflectorsare employed, which may be customized for particular applications byproviding different performance characteristics (e.g., high-irradiance,highly focused; short working distances to focused, long workingdistances; applications requiring large depth of focus while maintaininghigh-irradiance; and very wide-angle, more uniform irradianceapplications).

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of embodiments of the presentinvention. It will be apparent, however, to one skilled in the art thatembodiments of the present invention may be practiced without some ofthese specific details.

Notably, while embodiments of the present invention may be described inthe context of UV LED systems, embodiments of the present invention arenot so limited. For example, other wavelengths outside of the UV range,including deep UV, visible, infrared, microwaves and x-rays, alone or incombination, with one or multiple UV wavelengths, may also benefit fromthe architecture described herein. Also, varying wavelengths can be usedwithin the same light emitting device lamp to mimic the output ofmercury lamps by using UV A, B or C light emitting devices and visibleand/or IR light emitting devices. The high fill-factor characteristic ofembodiments of the present invention also enables inter-disbursement ofthe various wavelengths while avoiding pixelation effects on the workpiece surface which would likely result in deleterious process effects.Further, in accordance with various embodiments, the wavelength mixingwithin the macro-non-imaging-optical reflectors result in a uniform(non-pixelated) output beam from both a power density and wavelengthmixing standpoint.

For sake of brevity, embodiments of the present invention may bedescribed in the context of LEDs having the anode side on the bottom,those of ordinary skill in the art will recognize that the anode sidecould be on the top surface and/or both anode and cathode contacts couldbe on the top or the bottom. As such, references to anodic/cathodicstructures herein could be reversed (or could be electrically neutral)depending upon the particular implementation. Similarly, flip chip nowire bond LEDs, conductive substrate and non-conductive substrate LEDchips (such as those with the EPI layer on sapphire, aluminum nitride,silicon, zinc oxide or gallium nitride (GaN)), arrays and/or packageddevices may be considered. The EPI layer could be selected from thegroup of nitrides, oxides, silicides, carbides, phosphides, arsenides,etc.).

Terminology

Brief definitions of terms used throughout this application are givenbelow.

The phrase “average irradiance” generally refers to the irradiance valueacross a width of an output beam pattern projected on a work piecewherein the irradiance value falls to essentially zero on each side ofthe output beam pattern. In embodiments of the present invention, at 2mm from the window, a UV LED lamp head module produces average top hatirradiance of approximately 80 W/cm² (range 8-800 W/cm²). In embodimentsof the present invention, at 53 mm from the window, a UV LED lamp headmodule produces average irradiance of approximately 10 W/cm² (range 5-50W/cm²). In embodiments of the present invention, at 5 mm from thewindow, a UV LED lamp head module produces average irradiance ofapproximately 32 W/cm² (range 10-100 W/cm²) with an output beam patternhaving a width of approximately 8 mm and a “top hat” profile. In otherembodiments, at 65 mm from the window, a UV LED lamp head moduleproduces average irradiance of approximately 7 W/cm² (range 1-20 W/cm²)with an output beam pattern having a width of 25 mm and a “top hat”profile. In other embodiments, at 170 mm from the window, a UV LED lamphead module produces average irradiance of approximately 7 W/cm² (range0.5-10 W/cm²) with an output beam pattern having a width of 50 mm and a“top hat” profile. In some embodiments, an asymmetric top hat profile(tilted top hat) and output beam pattern having a width of 25 mm mayalso be produced at 65 mm from the window with a peak irradiance ofapproximately 8 W/cm² (range 1-20 W/cm²).

The terms “connected,” “coupled,” “mounted” and related terms are usedin an operational sense and are not necessarily limited to a directconnection, coupling or mounting.

The phrase “diffusion bonding” generally refers to a method of joiningmetals similar to welding, but relies only on the surface diffusing intoone another as a means of “welding.” For example a diffusion bondingprocess may bond layers of usually substantially similar materials byclamping them together, sometimes with an oxidation inhibiting platingsuch as nickel, and subjecting the layers to extremely high temperaturesof around 1,000 degrees C. (range 500-5,000 degrees C.), and therebymolecularly intermixing the surfaces and forming a substantiallymonolithic material wherein the grains are intermixed and often thebond-line is substantially indistinguishable from the bulk material, andthe properties of the diffusion bonded materials do not differsubstantially from bulk non-diffusion bonded materials in terms ofthermal conductivity and strength. Diffusion bonding could have somesimilarities to sintering. Thin layers of silver plating on the order ofmicrons may also be employed to facilitate the ease of bonding of thelayers. This later process may have some similarities to soldering.

The phrase “directly mounted” generally refers to a mounting in which nosubstantial intervening and/or thermally impeding layer is introducedthe two things being attached or affixed. In one embodiment, an LEDarray is mounted to a common anode substrate provided by a surface of amicro-channel cooler with a thin solder layer. This is an example ofwhat is intended to be encompassed by the phrase “directly mounted.” So,the LED array would be considered to be directly mounted to the commonanode substrate. Examples of thermally impeding layers would includebulk substrate material, foil, thin-film (dielectric or conducting), orother material (other than a thin solder layer) introduced between thetwo things being attached or affixed.

The phrase “high irradiance” generally refers to an irradiance ofgreater than 4 W/cm². According to embodiments of the present invention,peak irradiance levels achievable are approximately on order ofmagnitude to several orders of magnitude beyond the levels of currentstate-of-the-art UV LED curing systems while maintaining both highefficiency and long life of the LEDs. As described further below, inaccordance with various embodiments, the irradiance on the work piece issubstantially devoid of deleterious pixelation and/or gaps found incurrent UV LED curing systems. Meanwhile, it is to be noted most UV LEDlamp manufacturers measure peak irradiance at the window, whereas invarious embodiments described herein it is measured at the work piecesurface. Measurements at the window are essentially meaningless as thework piece is not typically located at the window.

The phrase “high fill-factor LED array” generally refers to an LED arrayin which the LEDs are closely spaced and the light emitting area (activeregion) exceeds 50% (often exceeding 90%) of the area (length×width) ofthe LED array. Depending upon the particular implementation, the fillfactor of an LED array may be greater than 60%, 70%, 80%, 90% or 99%. Inone embodiment of the present invention, LEDs within LED arrays arespaced less than 20 microns edge-to-edge and in some instances 10microns edge-to-edge, with a range of edge-to-edge distances from 1-100microns (zero micron spacing could be considered for a completelymonolithic LED). Both inorganic as well as substantially organic LEDsare contemplated.

The phrases “in one embodiment,” “according to one embodiment,” and thelike generally mean the particular feature, structure, or characteristicfollowing the phrase is included in at least one embodiment of thepresent invention, and may be included in more than one embodiment ofthe present invention. Importantly, such phases do not necessarily referto the same embodiment.

The term “irradiance” generally refers to the radiant power arriving ata surface per unit area (e.g., watts or milliwatts per square centimeter(W/cm² or mW/cm²).

The phrase “light emitting area” generally refers to an active region orthe epitaxial region of a light emitting device or array.

The phrase “light emitting device” generally refers to one or more lightemitting diodes (LEDs) (emitting substantially incoherent light) and/orlaser diodes (emitting substantially coherent light) whether they beedge emitters or surface emitters. In various embodiments of the presentinvention, light emitting devices may be packaged or bare dies. Apackaged die refers to a device that not only consists of the bare die,but usually also consists of a substrate to which the die is mounted(usually soldered) to facilitate the traces for electrical in and outcurrent paths, as well as thermal paths, and usually a means forattaching a lens and/or reflectors, an example of which would be theLexeon Rebel available from Philips, USA. Bare light emitting devicescould have a vertical structure or a horizontal structure and have anelectrically conductive substrate or a non-conductive substrate.According to one embodiment, bare light emitting device dies (i.e., diesexcised directly from wafers that have epitaxial grown p-n junctions)are bonded (usually soldered) directly (without an additionalsignificantly thermally impeding layer) to at least one diffusion bondedlayer of a high thermal conductivity material (selected from the groupof copper, Glidcop, BeO, Si, GaN, AlN, Al₂O₃, Al, Au, Ag, graphite,diamond and the like), which is in itself, in various embodiments of thepresent invention, usually a layer of a multi-layer laminate forming amonolithic diffusion bonded micro-channel cooler structure. The laminatedoes not necessarily have to be diffusion bonded as the bonding processcould be selected from soldering, brazing, gluing, etc. In otherembodiments, a submount may be used. LEDs include flip chip no wire bondLEDs, conductive substrate and non-conductive substrate LED chips (suchas those with the EPI layer on sapphire, aluminum nitride, silicon, zincoxide or gallium nitride (GaN)), arrays and/or packaged devices.

The phrase “light emitting diode” or the acronym “LED” generally referto a semiconductor device containing a p-n junction (the junctionbetween a p-type semiconductor and an n-type semiconductor) designed toemit specific narrow band wavelengths within the electromagneticspectrum via a process known as electroluminescence. In one embodiment,an LED emits incoherent light.

The phrase “low fill-factor LED array” generally refers to an LED arrayin which the LEDs are sparsely arranged and do not exceed approximately50% of the surface area of the LED array.

The phrase “low irradiance” generally refers to an irradiance of around20 W/cm² or less. UV LED systems rated at less than 4 W/cm² are nottypically sufficient for most curing applications other than pinning(e.g., ink setting).

The term “macro-reflector” generally refers to a reflector having aheight of greater than or equal to 5 mm. In some embodiments,macro-reflectors may range from 5 mm to over 100 mm.

The term “optical power density” generally refers to a measure ofoptical power per unit area. One measure of optical power density may bedetermined by measuring optical power at the surface of photon emittingareas of an LED array and determining a ratio of photon emitting areasto non-photon emitting areas (dead areas) for the LED array. In oneembodiment, the optical power density at the emitting surface of the LEDarray is at least 100 W/cm². Depending upon the particularimplementation, the optical power density may range from 1-10 W/mm².

If the specification states a component or feature “may”, “can”,“could”, or “might” be included or have a characteristic, thatparticular component or feature is not required to be included or havethe characteristic.

The phrase “patterned circuit material layer” generally refers to alayer of electrically conductive material usually containing metalselected from the group of copper, silver, gold, titanium, tungsten,nickel and may also contain electrically conductive polymers that arepatterned (e.g., direct or via lithographic means) onto a substrate(e.g., ceramics, dielectrics, semiconductors and/or polymers).

The phrase “peak irradiance” generally refers to the maximum irradiancevalue across a width of an output beam pattern projected on a workpiece. In embodiments of the present invention, at 2 mm from the window,a UV LED lamp head module can achieve a peak irradiance of approximately84 W/cm² (range 50-100 W/cm²). In embodiments of the present invention,at 53 mm from the window, a UV LED lamp head module can achieve a peakirradiance of approximately 24 W/cm² (range 10-50 W/cm²).

The phrases “radiant energy density,” “total output power density” or“energy density” generally refer to the energy arriving at a surface perunit area (e.g., joules or millijoules per square centimeter (J/cm² ormJ/cm²)).

The term “responsive” includes completely or partially responsive.

The phrases “top hat beam cross-section profile,” “top hat profile” andthe like generally refer to a beam profile which when projected on to awork piece applies a uniform intensity well-defined spot onto the workpiece and enables sharp and accurate transitions on the work piece beingprocessed. Top hat profiles may also be asymmetric. For example, betweenthe abrupt boundaries there may be a positive or negative slope or theremay be multiple peaks and valleys between the abrupt boundaries.

The phrase “top hat irradiance workpiece pattern,” “top hat pattern” andthe like generally refer to an irradiance pattern on a workpiece inwhich higher irradiance values are uniform over some distance withabrupt boundaries on either side as the irradiance decreases to lower ornegligible values. This is in comparison to a typical Gaussian orsmoothly tapered pattern, where the irradiance falls off from a centerpeak value more smoothly.

The phrase “total output power” generally refers to the aggregate powerin W/cm of output beam pattern length. According to one embodiment, at 2mm from the window, total output power of approximately 20.5 W per cm ofoutput beam pattern length is produced by each UV LED lamp head module.According to one embodiment, at 53 mm from the window, total outputpower of approximately 21.7 W per cm of output beam pattern length isproduced by each UV LED lamp head module.

The phrase “ultra high irradiance” generally refers to an irradiance ofgreater than 50 W/cm² at a work piece. In one embodiment, a UV LED lamphead module can achieve peak irradiance of greater than 100 W/cm² atshort working distances (e.g., ˜2 mm with a range of 0.1 to 10 mm). Inview of rapidly advancing power output and efficiency of LEDs, it isreasonable to expect peak irradiances achievable to improve by more thanan order of magnitude in the coming decades. As such, some of today'shigh irradiance applications will be accomplished with air-cooled LEDarrays and others will take advantage of or be enabled by these higherirradiances for faster, harder or more complete cures and/or use lessphotoinitiator. Also unique in the context of various embodiments of thepresent invention is the ability to provide both ultra high peakirradiance, ultra high average irradiance, ultra high total irradiance(dose) and concentration of the dose (as compared to the prior art) thatis delivered to the work piece.

The phrase “UV curing process” generally refers to a process in which aphotoinitiator (PhI) will absorb UV light first, causing it to go in toan excited state. From the excited state, PhI will decompose into freeradicals, which then starts a photo polymerization. However, there isalways some amount of oxygen (1-2 mM) in the UV curable formulation.Therefore, the initial free radicals from PhI photo-decomposition willreact with oxygen first, instead of reacting with the monomer's doublebond of (typically an acrylate), because the reaction rate of PhI freeradical with oxygen is about 105 to 106 faster than that of the acylatedouble bonds. Furthermore, at very early stages of UV curing, oxygen inair will also diffuse into the cured film and also react with the PhI,which results in major oxygen inhibition. Only after the oxygen in UVcurable film is consumed can photo-initiated polymerization take place.Therefore, in order to overcome oxygen inhibition, a large amount offree radicals are required at surface of the cured film within a veryshort period of time; i.e., a high intensity UV light source isrequired. The absorption of the UV light intensity for a particularformulation depends on the UV light wavelength. Mathematically, theabsorbed UV light intensity (Ia) is given by Ia=I0×[PhI], where I0 is aUV light intensity from UV light source and [PhI] is photoinitiatorconcentration. At the same [PhI] levels, increasing I0 will increase Iaand thereby reduce oxygen inhibition. Stated another way, by using ahigh I0 light source less [PhI] can used, which is typically the mostexpensive portion of the formulation. The absorption of UV light followsthe well-known Lambert-Beer Law: A (absorption)=

cd, where

is the PhI extinction or absorption coefficient, c is the concentrationof PhI and d is the thickness of the sample (film to be cured). As seenfrom the below table, the efficiency of PhI light absorption variesgreatly with wavelength. In this case, at 254 nm, the efficiency ofabsorbing light is 20 times higher than that at 405 nm. Therefore, ifthe UV LED light intensity at 400 nm can be provided at 100 timestypical curing powers at shorter wavelengths (˜100 W/cm²), thephotoinitiator's efficiency difference in absorption of light can reduceoxygen inhibition.

1.95×104 at 254 nm,

1.8×104 at 302 nm,

1.5×104 at 313 nm,

2.3×103 at 365 nm,

8.99×102 at 405 nm;

FIGS. 2A-C provide isometric, front and side views, respectively, of anultra-high brightness UV LED lamp head module 200 in accordance with anembodiment of the present invention. According to one embodiment,ultra-high brightness UV LED lamp head module 200 produces ultra-highirradiance. Ultra-high brightness UV LED lamp head module 200 may beused to, among other things, photo polymerize, or cure inks, coatings,adhesives and the like. Depending upon the application, a UV curingsystem (LED UV emitting system) (not shown) may be formed comprising oneor more UV LED lamp head modules 200 and other components, including,but not limited to, LED drivers (internal or external to the UV LED lamphead module 200), one or more cooling systems, one or more main AC/DCpower supply systems (e.g., available from Lineage (now, a division ofGE of Niskayuna, N.Y.) or Power-One, USA, which are approximately 90%(or even approximately 97%) efficient and weighing about 1 kg.), one ormore control modules, one or more cables and one or more connectors (notshown).

According to one embodiment, the high brightness of UV LED lamp headmodule 200 allows a range of possible optical properties of the outputbeam (not shown) including: narrow width (e.g., ˜0.65 cm (range 0.1 to 2cm)) with high power density (e.g., ˜20.5 W per cm of output beampattern length (range 10-30 W)), wider widths (e.g., ˜3.65 cm (range 3to 10 cm) with greater depth of focus, or short or long workingdistances (with or without greater depth of focus), or even very wideangle/large area beam output patterns (with or without greater depth offocus). Output beam patterns with homogenous irradiance (e.g., top hat)across the width of the beam (as well as the length of the beam) patternmay be considered as well as asymmetric irradiance.

As discussed further below, according to embodiments of the presentinvention, the high brightness results from a high fill-factor (inexcess of 50%, and often in excess of 90%) LED array (not shown) and theLED array being operated at high electrical power densities, whichresults in a high irradiance output beam. The high electrical powerdensities result in high thermal densities (due to electrical to opticalconversion loses) that are effectively managed via various novelmethodologies that are described in detail below.

Ultimately, the UV LED lamp head module 200 is intended to replace notonly the current state-of-the-art UV LED lamps, but also the currentstate-of-the-art mercury lamps, due to the uniquely high irradiance andflexible optical output beam properties that a high brightness sourceallows. UV LED lamp head module 200 is also considered to be a “greentechnology” as it contains no mercury, and is also electrically veryefficient. This efficiency is partly derived from the inherentefficiency of LEDs compared to mercury containing lamps, but alsoderived in part from cooling methodologies, which are described below,that provide for very low thermal resistance between the LED junctionsand the cooling fluid (introduced into the UV LED lamp head module 200via inlet cooling tube 203 and evacuated from the UV LED lamp headmodule 200 via outlet cooling tube 204), thereby creating low junctiontemperatures that are needed for highly efficient and long lifeoperation of LED devices.

In this depiction, a housing 202 and a reflector 201 of the UV LED lamphead module 200 are illustrated. According to various embodiments, thehousing 202 of the UV LED lamp head module 200 is approximately 80 mm inlength×38 mm in width×125 mm in height. The length of the novel easilyswappable and field-replaceable reflector 201 that is chosen for a givenapplication would be substantially in the range of tens to hundreds ofmillimeters in length, but such reflectors are typically about 100 mm inlength, and provide working distances in the range of 0-1000 mm, buttypically between 2 mm to 65 mm, inclusive.

According to embodiments of the present invention, UV LED lamp headmodule 200 is designed to be used stand alone or serially in combinationwith one or more other UV LED lamp head modules. As described furtherbelow, multiple UV LED lamp head modules 200 are easily configuredserially in length from one head (module) (e.g., 80 mm), to perhaps 100heads (modules), for example, with a length of 8,000 mm. Multiple UV LEDlamp head modules 200 could also be configured serially in width.According to one embodiment, a unique feature of a length-wise serialcombination of UV LED lamp head modules 200 is that the output beam doesnot contain a substantially discernable loss of irradiance at eachinterface point at which the heads (modules) are butted up against eachother serially end-to-end to make a long output beam pattern at the workpiece surface even in short working distance (e.g., ˜2 mm) applications.

As described in further detail below, in one embodiment, reflector 201is factory swappable and preferably also field replaceable. Thereflector 201 may be machined from aluminum and polished, cast, extrudedmetallic or polymer, etc., or injection molded. The reflector 201 couldhave silver coatings and could have a dielectric stack of coatings. Thereflector 201 could have a single layer protective dielectric coatingusing deposition processes (e.g., ALD, CVD, sputtering, evaporation,sol-gel). The reflector 201 could be mechanically or electrolyticallypolished. It is contemplated that multiple UV LED lamp head modules 200may often need to be placed end-to-end in long length applications, likewide-format printing. In these cases, it is desirable that the projectedand/or focused beam created by the reflector 201 has nearly uniformirradiance along the entire beam path, especially in the areas betweenthe end-to-end configured UV LED lamp head modules 200 and/or LEDarrays, so that the coatings, inks, adhesives, etc. of the work pieceare uniformly cured. It should be noted that due to the high irradiancesprovided by embodiments of the present invention coating and inks, etc.,may have substantially less photoinitiator in them or essentially nophotoinitiator and cure in a similar matter to E-beam in thatelectromagnetic energy is supplied in a sufficient dose to cure thematerial without the aid of any appreciable photoinitiator.

In various embodiments, the irradiance of the UV LED lamp head module200 can be in excess of 100 W/cm² in short working distance (e.g., ˜2mm) applications, such as inkjet printing, to in excess of 25 W/cm² inlong working distance (e.g., 50 mm +) applications, such as clear coatcuring. According to one embodiment, the beam widths can vary, to meet avariety of applications and operating conditions, from around 1 mm wideto 100 mm wide or more, and the length, as stated previously can be asshort as the width of one head (module) (e.g., 80 mm) to as long as 100heads (modules) (e.g., 8,000 mm) or more. It should be noted that thelength of the beam could be shorter than the length of the UV LED lamphead module 200 if focusing reflectors or optics were so employed toaffect this beam shape. Curved or extended end caps may also beconsidered. External refractive or diffractive optics are alsocontemplated. Depending upon the particular implementation, the lengthof the UV LED lamp head module 200 could range from tens to hundreds ofmillimeters in length. The LEDs could range from approximately 0.3 mm²to 4 mm² or more and they could be rectangular, oriented in single longrows, multiple long rows or monolithic.

According to embodiments of the present invention, the efficiency of theLED array 330 of FIG. 3A is usually well in excess of 10-20%, and theoverall system efficiency (including heat exchanger or chiller, pump,and power supply losses, is usually well in excess of 5-10%). In thefuture, efficiencies of over 50% are contemplated.

Returning briefly to the inlet cooling tube 203 and the outlet coolingtube 204, these may constructed of, for example, extruded polyurethane,vinyl, PVC (available from Hudson Extrusions, USA) and the like andcould be ˜ 5/16 inch ID and ˜ 7/16 inch OD. In one embodiment, the tubes203 and 204 are of a polyurethane with high tensile strength and lowmoisture absorption. Tube fittings available from Swagelok, USA may beemployed or fittings from John Guest, USA. Depending upon the usageenvironment, it may be preferable to use more than one inlet coolingtube 203 and outlet cooling tube 204, such as perhaps ˜4 smaller inletlines and ˜4 smaller outlet lines (not shown). This may make for a lesscumbersome unit with smaller bend radiuses and may allow slightly moreevenly distributed coolant flow through the micro-channel cooler (notshown); however, the deep main inlet and outlet channels (not shown)within the UV LED lamp head module 200 essentially eliminate pressuregradients at the point of entrance to and exit from the preferablemicro-channel cooler channels (not shown). In one embodiment, coolantenters the UV LED lamp head module 200 via inlet cooling tube 203 atbetween 1-100 PSI and preferably between approximately 15-20 PSI at atemperature of between about 5-50 degrees Celsius (C) and preferably atabout 20 degrees C. and exits via outlet cooling tube 204 at atemperature of between about 10-100 degrees C. and preferably atapproximately 24 degrees C.

According to one embodiment, waste heat from various internal components(e.g., LED driver PCBs and LED array) of the UV curing system may bedissipated into the lamp body (not shown) and carried away by coolantflow to a heat exchanger and/or a chiller. An exemplary chiller isavailable from Whaley, USA. In one embodiment, the chiller utilizes ahighly efficient scroll compressor (available from Emmerson, USA).Depending upon the usage model, the chiller may be of the “split”variety in which the reservoir, pump, evaporator and controls arelocated inside a building housing the UV curing system, and the rest ofthe components, such as scroll compressor, fan, condenser, etc. arelocated outside the building (e.g., on the roof or on the side of thebuilding). It should be noted that many or all of the chiller or heatexchanger components may be operated in series or parallel or acombination of both for one or more UV LED lamp head modules 200 and/orsupply components. By way of example, one large chiller could beemployed for multiple UV curing systems that may have one or more pumpsand or reservoirs. An exemplary heat exchanger element for water to airis available from Lytron, USA. Any cooling solution could use a bypassarrangement so that differing pressure or flow rates could go throughthe evaporator and the micro-channel-cooler simultaneously.

According to one embodiment, the cooling liquid (coolant) compriseswater. The coolant may also contain one or more bio-fouling inhibitors,anti-fungicides, corrosion inhibitors, anti-freezing materials (e.g.,glycol) and/or nano particles (e.g., alumina, diamond, ceramic, metal(e.g., nano copper), polymer, or some combination) for enhanced heattransfer, and the coolant system could contain membrane contractors,oxygen getters and micron filters. Nano particles, such as titania,excited by UV lamp energy for the dual purpose of enhancing thermalconductivity and/or heat transfer and due to the resulting Photo-Fentonprocess the elimination of biological materials, such as funguses andthe like. Membrane contractors effectively reduce CO₂ in the water andhelp to maintain optimal pH for optimal corrosion resistance of coppermicro-channel surfaces.

In one embodiment, a sliding vane pump (available from Fluidotech,Italy) may be employed. It has a flow rate of greater than ˜4 GPM andpressure as high as ˜60 PSI. This flow rate is well-suited for themicro-channel cooler architecture described in connection with variousembodiments of the present invention (e.g., serial connection of 4 ormore 80 mm UV LED lamp head modules 200). The pump also is very quiet,compact, long lasting, and efficient, as it only consumes ˜0.25 KW. Invarious embodiments, redundant coolant pumps may be employed to reduceopportunities for a single point of failure. Average flow rate may beapproximately 0.75 GPM (range 0.1 to 10 GPM) per lamp head.

FIGS. 3A-B provide cut-away views of the UV LED lamp head module 200 ofFIG. 2A. From these views, it can be seen that an optical reflectorlayer 350 comprising reflector 201 is mounted to a body 305 enclosedwithin housing 202. According to one embodiment, body 305 is constructedfrom copper or a dielectric polymer material (e.g., PEEK; Torlon; LCP;acrylic; polycarbonate; PPS potentially filled with fillers, such asgraphite, ceramic, metals, carbon, carbon nanotubes, graphene,nano-sized or micron-sized flakes, tubes, fibers, etc.). Some of thesefilled resins are available from Cool Polymers of North Kingstown, R.I.The lamp body 305 may be machined with 5-axis milling or injectionmolded. Alternatively, body 305 may be injection molded and optionallysecondarily milled or drilled. As described further below, variouscomponents may be mounted directly or indirectly to the body 305,including, but not limited to, the housing 202, the reflector 201, anLED array 330, the micro-channel cooler (preferably forming part of thecommon anode substrate for the LED array 330), cathode claws 321 andanode bus body 315 a-b, and one or more LED driver printed circuitboards (PCBs) 310, which are preferably metal core PCBs (MCPCBs) and theanode bus body 315 a-b may serve as the metal core of the MCPCBs (a/k/acommon anode back plane). Molded or glued thermally conductive pads maybe inserted between the MCPCB and the flowing coolant in the outer sidewalls of the lamp body.

In the present non-limiting example, body 305 has formed therein a maininlet lamp body cooling fluid channel 360 and a main outlet lamp bodycooling fluid channel 361 both of which run the length of body 305. Themain inlet lamp body cooling fluid channel 360 is in fluid communicationwith the inlet cooling tube 203 via a first coolant inlet (not shown)formed in the base of the body 305. The main outlet lamp body coolingfluid channel 361 is in fluid communication with the outlet cooling tube204 via a second coolant inlet (not shown) formed in the base of thebody 305. The channels 360 and 361 are sized such that coolant flowssubstantially uniformly through a micro-channel cooler (not shown)disposed there between. In one embodiment, the first and second coolantinlets may be on opposite ends of the base of the body 305, across fromeach other, staggered, or some combination thereof to facilitate equaland uniform flow of coolant from the main inlet lamp body cooling fluidchannel 360 to the main outlet lamp body cooling fluid channel 361through the micro-channel cooler. In alternative embodiments, multipleinlet lamp body cooling fluid channels and multiple outlet lamp bodycooling fluid channels may be used.

In one embodiment, flow balance through the micro-channel cooler isachieved by designing the primary coolant inlet and exit manifoldchannels that run parallel to the longitudinal axis of the LED array 330to reach a level of pressure drop that is nearly homogeneous along theirlength by extending the channel depth to a point that the coolantpressure differential near the top of the channel (nearest themicro-channel cooler (not shown)) has reached a point of nearhomeostasis along the entire length of the channel by spreading out fromthe inlet port, or converging to the exit port by way of a very deepchannel. In other words, the exceedingly deep channels 360 and 361 givethe coolant sufficient time, hydraulic resistance and surface drag tospread out along the length of the micro-channel cooler and achieve asmall pressure differential near the top of each channel thereinresulting in balanced flow through each micro-channel under the LEDarray 330.

According to one embodiment, sub-assembly components of the LED driverPCBs 310, include, but are not limited to, LED driver controller ICs(not shown, which could also be part of a DC/DC converter system), FETs312, gates (not shown), inductors 311, capacitors (not shown), resistors(not shown) and cathode bus bars 304 a-b. As indicated above, in oneembodiment, the LED driver PCBs 310 are multi-layer metal foil (e.g.,copper)/dielectric layers on a metal (core) substrate (e.g., MCPCB)(available from Cofan, Canada) and are coupled (e.g., affixed viascrews) to the body 305 with an intervening thermal conduction compoundin order to dissipate the waste heat from the driver assemblies into thebody 305 where it is carried off by the coolant flow through the maininlet lamp body cooling fluid channel 360 and the main outlet lamp bodycooling fluid channel 361. In the present example, the channels 360 and361 extend deep enough in the body 305 to provide cooling to the areasubstantially under the FETs 312 and inductors 311, where a significantamount of waste heat is generated. Vias may be used to electricallyconnect the multi-layer metal foil layers.

In one embodiment, LED driver assembly PCBs 310 a-b, containing surfacemount electrical components and other semiconductor components are atleast 90% efficient. Exemplary high current capable and efficient LEDdriver ICs (not shown) are available from National Semiconductor USA(e.g., part LM 3434 or LM 3433 or a substantially equivalent). Linearand Maxim, USA also make similar parts. LED driver ICs (not shown) aresemiconductor junction p-n containing devices, preferably silicon based,that allow the buck conversion of a higher voltage/lower current inputto be converted to a lower voltage and higher current amenable to thehigh current LED driving conditions desired in various embodiments ofthe present invention. PWM may be employed.

Individual LEDs or groups of LEDs of the LED array 330 are driven bycorresponding segments of LED driver PCBs 310 a-b. For example, 4 groupsof 17 LEDs per side of the UV LED lamp head module 200 driven atapproximately 3 A (range 0.5 to 30 A) per LED and approximately 4.5-5V(range 2-10V). In such an embodiment, the LED array 330 comprises 68LEDs in 2 rows of LEDs (136 total), with opposite LED groupselectrically driven and/or controlled by corresponding LED driver ICs ataround 3A per LED resulting in an approximately 2 kW input per UV LEDlamp head module 200. Another non-limiting example would be 16 LEDs in15 groups×2, which may be driven at approximately 4 V and 40 A per group(range 1-10 V and 1-500 A) and have an input of only approximately 12 Vinto the LED driver PCBs 310 a-b.

In some embodiments, due to the high efficiency of the surface mountelectrical components and other semiconductor components, custom metalcore PCBs (MCPCBs) can be constructed such that they may be affixed,preferably with screws or other means, to the sides of the body 305, andbe conduction cooled through the interface material and into thethermally conductive body 305. The waste heat ultimately being removedby the convective transport of the coolant flow through the body 305.For example, two LED driver PCBs 310 a-b, one on each side of the body305, may be constructed on a 2.5 mm (range 0.1-10 mm) thick copper coreboard that has approximately 4-12 mil thermally conductive dielectricmaterial layers (available from Thermagon USA and/or Cofan, Canada). Inone embodiment, highly thermally conductive dielectric layers areinterposed between copper metal layers (e.g., 1-4 oz. copper foillayers) of the LED driver PCBs 310 a-b, which are affixed to body 305.Each LED driver PCB 310 a-b (e.g., ×2) may have 4 electrically isolatedcathodic segments corresponding to the locations of the 4 groups of LEDsisolated by flex-circuit sections (4 of which are shown in the cut-awayexploded view of FIG. 6—two of which are driven by opposing LED driverPCBs 310 a-b). In one embodiment, the LED driver PCBs 310 a-b and theflex-circuit sections are arranged orthogonal to each other. Anothernon-limiting example is that each side of the body 305 has one LEDdriver PCB 310 a-b affixed to each side with 4 separate LED drivercontroller ICs located on each PCB (8 LED driver controller ICs total,that in sum can be driven up to around 2 kW or more per (e.g., 80 mmlong) UV LED lamp head module 200). Again, by affixing the LED driverPCBs 310 to the sides of the body 305, the waste heat from the LEDdriver PCBs 310 a-b may be dissipated into the body 305 and carried awayby the coolant flow to the heat exchanger or chiller. In one embodiment,a thermally conductive grease or other compound may be placed betweenthe LED driver PCBs 310 a-b and the body 305. In alternativeembodiments, the LED driver PCBs 310 a-b could be attached to the body305 in a non-thermally efficient manner and be convectively cooled viafans.

According to one embodiment, a common anode substrate layer 317 isclamped between cathode claws 320 a-d and 321 a-d and anode bus body 315a-b. A monolithic U-shaped common anode is formed by anode bus body 315a-b (which are substantially parallel to each other) and the commonanode substrate layer 317 (which is substantially orthogonal to theanode bus body 315 a-b). In another embodiment, the common anodesubstrate 317 and the anode bus body 315 a-b may form a monolithicrectangular or square shaped common anode.

In one embodiment, one surface of cathode claws 320 a-d and 321 a-d issubstantially parallel to the cathode portion of the common anodesubstrate 317 and another surface is substantially parallel to a topsurface of the LED driver PCBs 310 a-b, thereby allowing the to makeelectrical contact between these two layers. Further details regardingthe assembly forming the common anode substrate layer 317, includingmounting mechanisms for affixing the cathode claws 320 a-d 321 a-d, theanode bus body 315 a-b, are provided below.

In the present example, reflector 201 is a large (macro: e.g., tens ofmillimeters in height), modular, non-imaging reflector structure havinga mid-portion 352 significantly wider than either entrance 351 or exitapertures 353. Such a structure is well suited to printing applicationswhere short stand-off distances (e.g., 2 mm) from the work piece to thereflector 201, and high irradiance (e.g., greater than ˜50 W/cm²) arebeneficial for high process speed, cure hardness and cure completeness(tack free). According to one embodiment, the entrance aperture of thereflector pair (e.g., entrance aperture 351) has an area that is 110%(range 100-150%) as large an area of the light emitting surface of theLED array.

In one embodiment, reflector 201 captures and controls approximately 90%or more (range 50-99%) of the light emitted by the LED array 330 andeach half of the elongate reflector 201 is an ellipse having a focalpoint on the opposite side of the centerline of the projected opticalpattern on the work piece, with the result of increasing the peakirradiance over a traditional shared focal point (along the projectedbeam centerline) design approach. Compound ellipses or other compoundparabolic shapes may also be considered. In one embodiment, reflector201 is designed to have a high angular extent of approximately 80degrees (range of 45-90 degrees).

Various embodiments of the present invention seek to produce ahigh-quality cure (e.g., 100% or nearly so) by producing both high peakirradiance and high total output power (e.g., approximately 184 W per UVLED lamp head module 200) as photo-initiators can be toxic (andexpensive) and uncured inks, coatings, or adhesives are undesirable. Asnoted above, high irradiance results in faster, deeper, and harder curedmaterials. Consequently, embodiments of the present invention, seek toachieve peak irradiance levels that are approximately ten times (ormore) the levels disclosed in current state-of-the-art UV LED (andmercury lamp) curing systems while also maintaining both high efficiencyand long life of the LEDs.

According to one embodiment, reflector 201 is easily factory swappableand preferably field-replaceable thereby allowing other reflectors to beattached to the body 305 of UV LED lamp head module 200 for differentapplications, which might fulfill different process goals/parameters. Inthe present example, reflector 201 is shown as an elliptical reflectorthat is of two-part construction, where the two major components are theopposing sides of one or more ellipses. Reflector 201 may be machined ona five-axis mill and then polished with a diamond grit polish or it maybe extruded metal and post polished, or it may be extruded polymerwithout the need for post polishing due to the prior polishing of themold cavity/extrusion die. As described above, reflector 201 may be ofmodular design, such that an application, such as ink curing on a flatsubstrate that demands a narrow projected focal beam “line” of highirradiance (output power density) could use a bolt on ultra-highintensity line generating reflector (not shown), whereas an applicationon a rough topological substrate that demands a longer depth of fieldcould require a reflector pair (not shown) specifically designed forthis longer depth of field (or longer depth of focus) that is easilyinterchanged with the high intensity reflector pair by simply unboltingthe previous reflector pair and bolting the new reflector pair in placeas described in more detail below. Similarly, a reflector pair may bespecifically configured for long working distance with high intensity orlong working distance with a wide area smooth intensity beam pattern(e.g., a top hat beam pattern) on the work piece. Locating pins betweenthe reflector 201 and the common anode substrate layer 317 may beemployed.

In one embodiment, the internal surface of the preferably injectedmolded polymeric reflector 201 is a silver vacuum-deposited coating withan ALD (atomic layer deposition) protective overcoat that is corrosionresistant due to the pin-hole free nature of the ALD process. The silvercoating may be deposited using various deposition processes (e.g., ALD,CVD, sputtering, evaporation, sol-gel). As polycarbonate is aninexpensive polymeric reflector resin, a vapor barrier should be placedon the polycarbonate before the silver is deposited so that the side ofthe silver coating facing the polymeric reflector substrate does notallow corrosive vapor (molecules) to corrode the silver from the insideout. Low vapor permeable resins (e.g., E48R (Zeon Chemicals, USA)) maybe considered. High temperature resins like Ultem and Extem areavailable from Sabic, USA. Also, vapor barriers (e.g., copper, ALD oxidecoatings) may additionally be considered and, deposited on the reflectorprior to the silver or aluminum coating. The ALD dielectric overcoat isselected from the group of oxides (e.g., Al₂O₃) or fluorides (e.g.,MgF₂) or some combination thereof. Alternatively, an HR coating on thereflector 201 can also be a dielectric overcoated aluminum coating on aninjection molded polymeric reflector. The dielectric coating ispreferably a single layer magnesium fluoride or silicon dioxide tunedfor peak reflectivity around the wavelength that is best suited to theapplication. A dielectric stack based on optical interference may beemployed for any of the above-mentioned configurations to increase peakirradiance in the selected wavelength range.

Embodiments of the present invention may employ secondary optics (notshown) for beam control and/or a window (e.g., a lens) 340 that has anantireflective (AR) coating. The AR coating is preferably a BAAR (broadangle antireflective) coating as the angles emitting from the exitaperture 353 may be in excess of 45 degrees, as such high angles wouldundergo significant deleterious reflection from the window surface ifsuch a BAAR coating was not used. High UV resistant acrylic for tanningbeds could be considered, but borosilicate glass is preferable forwindow 340 and secondary optics. In one embodiment, a window mount 341holds window 340 in place as described further below. According to oneembodiment, an o-ring (not shown) is situated between the window 340 andreflector 201. In one embodiment, the external housing for the reflector201 may be injection molded. In various embodiments, an inert gas ormicro-porous spheres (available from Zeolite, USA) may be used tocontrol water vapor. This vapor can be an issue for LED longevity shouldno encapsulant over the LEDs be employed. Current state-of-the-art doesnot allow for an LED encapsulant (such as high purity silicone) to beemployed as yellowing from the high photon energies of the short UVwavelengths is an issue. Silicone encapsulants from Schott (Germany)with low carbon content are known to be the least yellowing in existenceat this time.

For purposes of measuring a distance from the window 340 to a work piecesurface, it is to be understood that the window 340 has an inner surface(closest to the surface of the LED array 330) and an outer surface(closest to the surface of the work piece). Herein, distances to thework piece are generally measured with respect to the outer surface ofthe window 340.

FIGS. 4A-B provide magnified cut-away views of a bottom portion ofreflector 201 and a top portion of body 305 of the UV LED lamp headmodule 200 of FIG. 2A. In these views, LED array 330 and various aspectsof the common anode substrate layer 317 become apparent. Additionally,in these views, separator gasket 314 is depicted as being formed of aplurality of o-rings 420 and a preferred multilayer construction of theLED driver PCBs 310 a-b becomes visible.

As described in further detail below, in one embodiment, a micro-channelcooler 410 provides the common anode substrate layer 317. According toone embodiment, micro-channel cooler 410 is a diffusion bonded etchedfoil micro-channel cooler including a heat spreader layer (not shown)diffusion bonded to foil layers (not shown) having etched thereinvarious primary inlet/outlet micro-channels 411 and internalmicro-channels (not shown). While micro-channel cooling does have alaminar component in which the boundary layer is compressed, inembodiments of the present invention, impingement cooling (e.g.,turbulence) may result from etched coolant flow path shape and/ordirectional changes. An exemplary micro-channel cooler is illustrated byU.S. Pat. No. 7,836,940, which is hereby incorporated by reference inits entirety for all purposes. Micro-channel coolers meeting the coolingrequirements described herein are available from Micro-Cooling Concepts,USA. Those skilled in the art will recognize that various other coolingschemes may be employed. For example, macro-channel cooling and otherturbulent flow cooling paths (e.g., impingement, jet-impingement) ortwo-phase/nucleate boiling (or some combination), and cooling schemesmay be considered.

According to various embodiments of the present invention, one objectiveis to create and maintain a relatively isothermal state (e.g., junctiontemperatures within approximately ±1 degree C. and also generally amaximum average junction temperature of ˜40 degrees C. (range 30-200degrees C.) from end-to-end of the LED array 330. To achieve thisobjective, embodiments of the present invention attempt to balancecoolant flow through the micro-channel cooler 410 from front to back,top to bottom, end to end and/or side to side. In alternativeembodiments, the flow may be balanced or imbalanced to accommodatedesign needs. The coolant may flow through internal primary andsecondary channels (not shown) of the micro-channel cooler 410 invirtually any direction, selected from vertical, horizontal, orthogonal,parallel, etc., or any combination thereof, with respect to the bottomsurface of, as well as under, the LEDs of the LED array 330. Another wayof describing the orientation of the channels is with respect to the p-njunction plane, which is (in most LEDs) substantially parallel to thebottom surface of the LED.

Similarly, the internal primary and/or secondary channels they may beinterconnected with virtually any orientation of manifold(s) selectedfrom vertical, horizontal, orthogonal, parallel, diagonal, angular,by-pass, partial by-pass, etc., or any combination thereof, again withrespect to the orientation of the bottoms of the LEDs (or the p-njunctions of the LEDs). It is preferable that all, or almost all (near100%) of the coolant eventually flows from the top portion (e.g., maininlet micro-channel cooler cooling fluid channel 430 b) of main inletlamp body cooling fluid channel 360 through the micro-channel cooler 410to the top portion (e.g., main outlet micro-channel cooler cooling fluidchannel 430 a) of main outlet lamp body cooling fluid channel 361 in adirection that is orthogonal, or perpendicular, to the long-axis of theLED array 330 and/or micro-channel cooler 410. In one embodiment,micro-channel cooler 410 utilizes flow paths optimized by CFD to reduceflow velocities to such a level so as to greatly reduce erosion. In oneembodiment, coolant velocities of approximately 2 meters/sec. arepreferred to reduce erosion of the channels. Ceramic materials may beused for the channel substrate to even further eliminate erosionpotential.

As noted earlier, the main inlet lamp body cooling fluid channel 360 andthe main outlet lamp body cooling fluid channel 316 are sized such thatthe coolant flows uniformly through the etched foil internalmicro-channels, and so that preferably nearly all of the coolanteventually ends up running in a substantially perpendicular direction tothe long axis of LED array 330, in that any given molecule of coolantthat starts in main inlet lamp body cooling fluid channel 360 eventuallyends up in the main outlet lamp body cooling fluid channel 361, and so,essentially each molecule of coolant eventually flows substantiallyperpendicular to the long-axis of LED array 330 (substantially parallelto the short-axis of the LED array 330) as it traverses micro-channelcooler 410 and flows under the LEDs. By making the main inlet lamp bodycooling fluid channel 360 very narrow (e.g., approximately 1-4 mm andpreferably approximately 2.3 mm) wide and very deep (e.g., approximately1-10,000 mm and preferably about 100 mm), the resultant hydraulicresistance aids in uniform micro-channel flow in terms of balanced flowthrough substantially all or most of the internal channels ofmicro-channel cooler 410, whether or not they be primary, cross,secondary, manifold, etc. channels. It should be understood that thesechannels could have curves, s-bends, protrusion for turbulence, andperhaps narrow and widen and/or deepen as they traverse the space underLED array 330 in the direction that is substantially lateral or parallelto the short axis of LED array 330. Again, the orientation of any givenmicro-channel can be in any orientation (as well as flow direction) withrespect to the orientation of the p-n junctions of the LEDs.

As described in further detail below, LED array 330, comprising lightemitting devices, such as LEDs or laser diodes, are mounted to themicro-channel cooler 410. In one embodiment, the range of the number ofLEDs along the length of the micro-channel cooler is 2-10,000, and thesize of each LED is approximately 1.07, 1.2, 2, 4 mm square (or 2×4 mm),range of 0.1-100 mm. The aspect ratio of the width to length ispreferably about 1:68 to 1:200, but the range may be 1:10-1:1,000. Itshould be noted that the LED arrays may not be high aspect ratio and maybe substantially square, substantially rectangular, substantiallycircular or other geometries. Exemplary LEDs are available fromSemiLEDs, USA. SemiLEDs' LEDs have a unique (often plated) coppersubstrate which is advantageously bonded to the copper (or ceramic)micro-channel cooler 410, thereby maintaining the thermal and costadvantageous of this high thermal conductivity material. According toone embodiment, the size of the LEDs employed are 1.07×1.07 mm squareand the LED array 330 comprises an array of 68 LEDs long by 2 LEDs wide.

Nichia, Japan is also an exemplary LED provider that commonlymanufactures horizontal structure LEDs versus SemiLEDs' common verticalstructure LEDs. In one embodiment, one or more of the seriesed groups ofLEDs or the entire LED array may be implemented with horizontalstructure LEDs that have anode and cathode pads on a top of surface,such as on top of a non-conductive substrate, such as sapphire. Forexample, a cathode wire can be coupled to multi-layer flex circuit 1403at one end of the series and an anode wire can be coupled to multi-layerflex circuit 1403 at the other end of the series without the use of asubmount for the particular seriesed group of LEDs.

In one embodiment of the present invention, the LEDs of LED array 330are placed substantially in electrical parallel, or have at least twoLEDs in parallel, on a preferably common anode substrate. This is a verythermally efficient manner of connection, as no thermally impedingdielectric layer between the base of the LED and the substrate need beadded for the purpose of electrical isolation as is needed in aconventional series configuration or conventional series/parallelconfiguration. Nonetheless, it should be noted that any of theseconfigurations could be considered in various embodiments, as well as apurely series arrangement, or a series/parallel arrangement. While adielectric layer could substantially add to overall thermal resistance,thereby raising the junction temperature of the device(s) and adverselyimpacting output power and/or efficiency, it is contemplated that a verythin dielectric layer on the order of a few microns thick or less may begrown by means such as atomic layer deposition and provide a very lowthermal impedance layer over a material such as copper for the purposeof electrical insulation in a series/parallel type arrangement. Thisdielectric could be selected from the group of oxides, nitrides,carbides, ceramics, diamond, polymers (ALD polyimide), DLC, etc.

According to various embodiments of the present invention, one objectiveis to maintain extremely low thermal resistance between the epitaxialp-n junctions of the LEDs, or at least the bottom of the preferably baredie, that is approximately 0.015 K-cm²/W, but the range may be 0.0010-15K-cm²/W, and is often around 0.024 K-cm²/W. Very thin layers of foil,bond pads, traces, etc. of either metallic, dielectric, ceramic, orpolymer layers may be considered, but are not optimal due to theincrease in thermal resistance that results from these additionallayers, which inevitably results in an increase in junctiontemperatures, with a corresponding decrease in efficiency. Various meansfor decreasing current droop associated with the epitaxial structuregrowth and design, such as thicker n or p capping layers may beemployed, as well as other state-of-the-art means (e.g., new quantumbarrier designs, reducing non-radiative recombination centers, etc.)found in recently published scientific journals, and authored byemployees of Philips, Netherlands, and RPI, USA, and others (see, e.g.,Rensselaer Magazine, “New LED Drops the ‘Droop’” March 2009 and CompoundSemiconductor Magazine, “LED Droop: Do Defects Play A Major Role?” Jul.14, 2010, both of which are hereby incorporated by reference in theirentirety for all purposes). Epitaxial growth on native GaN wafers andeven polar GaN wafers are currently considered to reduce or eliminatecurrent droop.

As such, in accordance with various embodiments, an extremely lowthermal resistance path exists between the LED junction and the etched(e.g., chemically etched) foil layers that contain flowing liquid in thepreferably chemically etched micro-channels, because the LEDs aredirectly mounted (preferably with 2.5 um thick SnCu solder), and theheat spreader (if employed) and foil layers are thin, and theypreferably do not enlist an intervening dielectric layer. Other etchingor lithographic or machining processes may also be considered in themanufacture of the micro-channels.

According to one embodiment, the LEDs of LED array 330 are bondeddirectly (i.e., no substantial intervening layer (whether bulk material,foil, thin-film, or other material) between the LED and themicro-channel cooler 410 other than, for example, a thin pre-sputteredsolder layer that is preferably pre-applied (e.g., by sputter depositionmeans) to a bottom surface of the LEDs.

As described in further detail below, a separator gasket 314 may beformed by one or more o-rings 420 to seal the common anode substratelayer 317 to the body 305 and also prevent coolant bypass substantiallydirectly under the LED array 330. While in this and other figures, theo-rings 420 a-c do not appear to be compressed, it will be appreciatedthat in real-world operation, they would in fact be compressed toperform their intended function of preventing fluid by-pass betweenchannels or into the external environment. In the present example,separator gasket 314 is substantially parallel to, and in the samez-axis plane, as the bottom surface (opposite to the light emittingdirection) of the diffusion bonded foil layers (not shown) of themicro-channel cooler (whether layered vertically or horizontally). Thecross-section of the separator gasket 314 is preferably substantiallyround, may be made of a soft durometer silicone, and may be manufacturedby Apple Rubber USA. In alternative embodiments, the cross-section ofthe separator gasket 314 may be square or rectangular.

With reference to the multilayer construction of the LED driver PCBs 310a-b illustrated in the present example, in one embodiment, copper (oraluminum, polymer, filled polymer, etc.) metal core PCB boards that areapproximately 2.5 mm thick (range 0.1-10 mm) and available from CofanCanada are constructed of multiple layers to keep the size of the PCB ata minimum. The high power FETs and gate drivers and inductors andresistors and capacitors may be mounted on the preferably Thermagon USAlayer that is closest to the metal core. In fact, in some embodiments,this layer could be windowed or cored so that the FETs (or other driverPCB components) can be mounted directly to the metal core with orwithout attachment screws. The LM 3434 or LM 3433 (examples only) seriesLED common anode drivers available from National Semiconductor USA couldalso be mounted as close as possible to the metal core as well, meaningthat a minimal dielectric layer thickness (if any) may exists betweenthe components and metal core. Equal trace path lengths and closecomponent spacing should also be considered for efficient electrical andstable operation. Custom wound inductors can increase drive sub-assemblyefficiency greatly. The inductors could be oriented in such a manner asto make the magnetic fields of the separate drivers (e.g., 8 or 15) witha preferable common backplane (e.g., anode body 315 a-b) that also maybe shared with the common anode substrate 317 of the micro-coolerflex-circuit assembly advantageously interacting with each other toincrease the efficiency of the preferably constant current driver(though a constant voltage driver may be considered, especially withspecial circuitry). Pulse width modulation (PWM) constant currentdrivers may be considered, although, PWM can have a deleterious effecton LED lifetime at high currents due to current ripple, additionalcapacitors between the inductors and the LEDs should be considered.Alternatively, an iron substrate could be placed between the inductorsto reduce undesirable interaction between the inductors or othercomponents that may be orientation and spacing dependent. Mostpreferably, shielded, off-the-shelf (OFS) inductors from VASHAY, Indiacan be considered.

On the backside of the lamp body 306 (the side where the main inputwater and electrical energy in/out sources are located) the preferablymetal (copper, aluminum, composite) MCPCB cores can have a screwed orsoldered tie bar (or anode cross plate between the two MCPCB (PCBs withmetal cores available from Cofan, Canada) cores to make a space and/orstrong mounting plate for a single wire connection for the anode thatwill then run to the main AC/DC front end power supplies that areconnected to the AC mains.

In one embodiment, the metal cores of the LED driver PCBs 310 a-b arethe ground plains—there may be more than one ground plane on each LEDdriver PCB 310 a-b. As such, the edge of the PCB is preferably clampedor soldered to the ground plain of the common anode substrate layer 317.This is preferably accomplished by allowing the common anode substratelayer 317 to extend, or hang over, each side of the body 305, such thatthe anodic side of the common anode substrate layer 317 can touch and bein electrical communication with the anode side (edge) of the LED driverPCBs 310 a-b, and the cathodic sides of the common anode substrate layer317 (e.g., the top foil layer) can preferably touch and be in electricalcommunication with the proper top cathode area of the individualcathodic segments that are in electrical communication with the LEDdriver PCBs 310 a-b.

FIGS. 5A-B provide further magnified views illustrating LED array 330and its interface with common anode substrate 317 of the UV LED lamphead module 200 of FIG. 2. In these views, the high fill-factor of theLED array 330, the electrical coupling of the individual LEDs, theproximity of the base of the reflector 201 to the surface of the LEDsand the various layers of a flex-circuit 510 become apparent.Additionally, in these views, the preferably vertically-oriented foillayers of the micro-channel cooler 410 become visible.

According to one embodiment, common anode substrate layer 317 mayinclude a micro-channel cooler 410 for transferring heat from LED array330, an integrated etched capping layer 525 and a solid capping layer530. In one embodiment, the width of the micro-channel cooler 410 isonly slightly (e.g., less than about 400 microns (range 50-2,000microns)) wider than the LED array 330. In one embodiment, the totalwidth of the micro-channel cooler 410 is about 1.2 times (range 1, 1.1,1.3, 1.4, 1.5, 1.6, 1.7, 1.9, 2, 2.1, 2.2, 2.3, 2.4 to 2.5×) the totalwidth of the LED array 330. In the present context, computer modelingsuggests that increasing the total width of the micro-channel cooler 410to a width of nearly double (2×) the width of the LED array 330decreases the peak thermal resistance by only about 5%.

The micro-channel cooler 410 may include a heat spreader layer 540(a/k/a thermal diffusion layer or a heat dissipating top surface) (e.g.,approximately 125 microns thick (ranging from less than 500 microns,less than 250 microns, less than 200 microns, less than 150 microns,less than 100 microns, less than 50 microns, to less than 25 microns),below a top surface of the micro-channel cooler 410, a plurality ofprimary inlet/outlet micro-channels (e.g., primary inlet micro-channel411) and various inlet manifold passages, heat transfer passages andoutlet manifold passages. Notably, in the present context, the heatspreader layer 540 really provides little true heat spreading; however,it does provide an extremely short thermal diffusion length (distancebetween the bottom of the LEDs and the closest of the heat transferchannels (not shown) of the micro-channel cooler 410). Exemplary heattransfer channels, their orientation, flow directions and dimensions areprovided by U.S. Pat. No. 7,836,940, incorporated by reference herein.

The top surface of the micro-channel cooler 410 may couple themicro-channel cooler 410 with LED array 330. Primary inletmicro-channels (not shown) may be configured to receive and direct afluid into internal passages within the micro-channel cooler 410,including heat transfer passages. The heat transfer passages may beconfigured to receive and direct the fluid in a direction substantiallyparallel to the top surface and substantially perpendicular variousinput and output manifold passages. The outlet manifold passages may beconfigured to receive and direct the fluid to one or more primary outletmicro-channels (e.g., primary outlet micro-channel 411).

In one embodiment, micro-channel cooler 410 may be formed from aplurality of etched foil sheets (e.g., foil sheet 520) having formedtherein the internal passages and manifolds for directing coolant flow.In the current example, a monolithic micro-channel cooler body is formedby diffusion bonding the combined etched capping layer 525 and solidcapping layer 530 to micro-channel cooler 410. As shown in FIG. 5A, foillayers of the etched capping layer 525 are preferably thicker than thefoil layers 520 of the micro-channel cooler 410. In one embodiment, thecapping layers 525 and 530 could be machined.

In an embodiment in which the diffusion bonded foil layers (e.g., foillayer 520) are vertically stacked (and diffusion bonded together) withtheir edges lying under the bottom portion of the LEDs as illustrated inFIGS. 5A and 5B, the LEDs are preferably bonded directly to thevertically-oriented micro-cooler (with or without plating such as ENIG,or ENEPIG, Superior plating, USA), and preferably two machined pure(C101 or C110 ) copper blocks, with mirrored (matching) macro-coolantflow and/or coolant directing channels, “pinching” the vertically laidup etched diffusion bonded micro-channel cooler. Each copper block(which could be in and of itself be a stack of diffusion bonded foils ora solid block) is diffusion bonded to opposing sides of the verticallystacked foil micro-channel cooler 410 in one step. In other words, thefoil layers and blocks are preferably diffusion bonded all in one step.The resultant stack is then preferably machine excised, and the assemblycan then be referred to as the micro-channel cooler assembly, whereasportions of the micro-channel cooler assembly may be referred to asouter capping layer portions (525 and 530) and a micro-channel coolerportion 410. The micro-channel cooler assembly (e.g., outer cappinglayer portions 525 and 530) is/are preferably drilled before performinga machined excision process and before surface finishing process(es)(e.g., a plating process). If a plating process is utilized for thepurpose of providing a solderable surface for the LEDs and/or a wirebondable surface for the wires that attach to the LED bond pads on thepreferable LED top-side, a machined polymer panel is preferably providedthat allows for an o-ring groove (preferable utilizing the sameaforementioned separator gasket/o-ring design) that allows themicro-channel cooler assembly to be clamped to the polymer block and putinto a plating bath with out solution getting into the ID of themicro-channels. This process may also allow for a non-corrosive surfaceto be plated in regions that the anode and/or cathode bus bars 304 a-bmay be eventually clamped or soldered to in the end product. The LEDdriver PCBs 310 a-b may also be edge plated for corrosion reduction andlow voltage drop purposes.

The micro-channel cooler assembly could undergo a quenching or annealingor precipitation hardening process so that pure hardened copper (whichhas an approximately 10% higher thermal conductivity than Glidcop) couldbe used in the foil layers (e.g., foil layer 520). Pure copper wouldenhance solder wetting.

In an embodiment in which the diffusion bonded foil layers (e.g., foillayer 520) are oriented horizontally, the micro-channels ofmicro-channel cooler 410 may be etched in the same plane as the bottomof the LEDs (e.g., LED 531) so the primary inlet/outlet micro-channels(e.g., channel 411) can be etched or even machined in the foil layers.The internal micro-channels of micro-channel cooler 410 may be formedthrough all or substantially all of the diffusion bonded foil layers(e.g., foil layer 520) substantially as deep as the thickness of all thelayers together and/or stopping near or at the bottom of the heatspreader layer 540 may be considered.

Turning now to the positioning of reflector 201, it is preferable thatdielectric spacer layer 514, such as polyimide film, be placed betweenthe bottom surface of the reflector 201 and the micro-channel cooler410. This insulates the reflectors from the micro-channel cooler 410both thermally and electrically, as well as provides a space for thewires (e.g., wire 530) from the LEDs (e.g., LED 531) to fit under thereflector 201 and have the crescent end of the wire affixed to thepreferably gold containing plated copper foil layer 513 that is part ofthe flex-circuit assembly 510, which is directly bonded to themicro-channel cooler 410. As such in one embodiment, the dielectricspacer layer 514 is at least as thick as the thickness of the wires(e.g., wire 530).

Using an automated die bonder such as a Datacon, Austria, MRSI, USA orPalomar, USA with a tamping tool or even a capillary tool, the wires(e.g., wire 530) can be automatically tamped (bent) down in such a wayas to lower the wire loop until it is substantially parallel (andperhaps even touching the foil layer on top of the polyimide layerbefore the crescent termination point) to the flex-circuit510-polyimide/copper foil layer(s) (a/k/a conductive circuit materiallayer). The flattened wire does not touch the anode surface or the edgeof the LED (e.g., LED 531) as a short could otherwise result. Othermanual and/or automatic means may be considered, such as one longtamping tool that tamps all of the wires in one step, or the edgereflector itself with or without a dielectric coating could be employedfor this tamping purpose. The primary purpose of this wire-bending stepis to allow the reflectors to be placed in very close proximity to theLEDs (e.g., within at least a wire diameter) and to eliminate chafing,touching, or shorting to the reflector 201. The reflectors (e.g.,reflector 201) may be preferably designed with a non-imaging softwaretool such as Photopia available from LTI Optics, USA. The reflectors mayhave different operational characteristics such as short to long workingdistances, or short to long depths of field. They should be easilyreplaceable such that they are modular and interchangeable and such thatthey provide the end user with the maximum in operational flexibility.In one embodiment, external dimensions of reflector 201 does notsubstantially change for reflectors configured for differing stand offdistances. For example, as described further below, a reflectoroptimized for a 2 mm focal plane may have substantially similar externaldimensions of a reflector optimized for a 53, 65 or 170 mm focal plane.

The reflectors (e.g., reflector 201) may be injection molded fromacrylic, polysulphone, polyolefin, polyetherimide, etc. They may becoated with aluminum and/or silver with a dielectric enhancement layersat DSI, USA. They may also be extruded from a polymer or metal. Itshould be noted that monolithic reflector halves 201 running the lengthof the entire assembly of all the UV LED lamp head modules 200 placedend to end (serially in length) may be employed. These long reflectorscould have polished and coated end cap(s) at each end. They could be5-axis machined from 6061 Al and polished with diamond and a horse hairbrush (as the reflectors may be polished) and coated with, for example,a single layer of MgF2 or SiO₂ optimized, for example (as allaforementioned examples) at 390-400 nm.

One skilled in the art could conceive of any length of LED array 330,reflector 201 and lamp body 305. As described above, one possible lengthof lamp body 305 is approximately 80 mm. This allows for approximately60 45 mil per side LEDs or 68 40 mil per side LEDs, both preferably intwo rows with about a 15 micron (range 5-50 um) gap (e.g., gap 532)between the two rows. A single row or multiple rows (from 1-n) LEDs maybe considered. Even rectangular LEDs that have a longer length along thelong-axis of the LED array may be considered. Along the long-axis, it ispreferable to have less than a 25 micron (range 5-100 um) gap (e.g., gap533). In one embodiment, center-to-center distances between LEDs of theLED array 330 are approximately 10 to 20 microns greater than thecombined edge lengths of neighboring LEDs.

Embodiments of the present invention take into consideration the overallz-axis stack up of the metallic and dielectric layers of theflex-circuit 510 (minus the dielectric spacer layer 514), plus the wirelayer thickness (diameter of each wire or thickness of each wire strip)running above the preferably cathode flex-circuit layer 513 and runningto the rectangular-shaped cathode wire bond pad 534 shown beneath theball bonds of the wires (e.g., wire 530) on the preferably top surfaceof the LEDs.

In one embodiment, the total z-axis stack up is not much thicker thanthe thickness of the LEDs (a/k/a the LED layer). In various embodimentsof the present invention, the LED layer may have a thickness ofapproximately 145 microns and ranging from a thickness of approximately250 microns or less, 200 microns or less, 150 microns or less, 100microns or less, 50 microns or less to 25 microns or less.

In various embodiments of the present invention, in which theflex-circuit layer 510 includes the dielectric spacer layer 514, theflex-circuit layer may have a thickness of approximately 7.8 mil or lessand ranging from a thickness of approximately 20 mil, 15 mil, 12 mil orless, 10 mil or less, 5 mil or less to 3 mil or less.

In various embodiments of the present invention, in which theflex-circuit layer 510 excludes the dielectric spacer layer 514, theflex-circuit layer may have a thickness of approximately 5.3 mil or lessand ranging from a thickness of approximately 10 mil or less, 8 mil orless, 2.5 mil or less to 0.5 mil or less.

In one embodiment, the total z-axis stack up is not much thicker thanthe thickness of the LEDs (a/k/a the LED layer), which could be thethickness of the bare LED or a packaged LED. In various embodiments ofthe present invention, the LED layer may have a thickness ofapproximately 145 microns and ranging from a thickness of approximately250 microns or less, 200 microns or less, 150 microns or less, 100microns or less, 50 microns or less to 25 microns or less.

In one embodiment, a bottom surface of the optical reflector 201 isbetween approximately 1-1.5× the thickness of the wire layer above a topsurface of the light emitting device array layer. In another embodiment,a bottom surface of the optical reflector 201 is between approximately0.33-0.5×the thickness of the LED layer. This allows reflector 201 tofit in close proximity to either or both the edge of the LEDs or inrelation to the top surface of the LEDs, which thereby maintainsirradiance by maximizing the number of emitted photons that arecontrolled by the reflector 201 and minimizing the number of emittedphotons that escape the reflector 201 by going underneath the reflector201. Locating reflector 201 close to the LED edge also allows for a morecompact reflector in terms of height. This proximity of the reflector201 to the LED array 330 also allows for a shorter length cathode layer513 of the flex-circuit 510, which also allows the cathode layer 513 tobe thin and still carry high current without too much impedance. Thefurther the reflector edge gets from the LED, the taller the reflectorneeds to be according to commonly known optical principles. Althoughslightly higher irradiance could be achieved with taller reflectors,taller reflectors may be impractical in certain implementations.

Additionally, the flex-circuit 510 is inexpensive to manufacture and isvery compact and thin, as such, it is well suited to usage in thecontext of embodiments of the present invention in which the overallz-axis stack up of the metallic and dielectric layers of theflex-circuit are desired to be minimized. Lenthor, USA, is an example ofan excellent flex-circuit manufacturer. In one embodiment, as describedfurther below, flex-circuit 510 may extend beyond the micro-channelcooler assembly and may be connected (directly or indirectly) toexternal DC/DC and/or power supplies.

As described earlier, another novel feature of embodiments of thepresent invention includes the use of a preferably diffusion bonded(though the layers may be soldered or glued or brazed) preferably etchedfoil micro-channel cooler 410 that preferably has a high aspect ratio ofat least one short laterally etched channel(s) (across the shortdirection (width) of the LED array 330) that may be in thermal paralleland preferably arrayed in a side-by-side fashion over a long length, inwhich the coolant flows across and underneath the LED array 330 in thedirection preferably substantially parallel to the shortest dimension(s)of the array 330, usually the width not length dimension. In otherembodiments, the coolant may flow in a direction along the length of theLED array 330 and/or cooler 410, and it may flow vertically (towards thebottom surface of the LEDs) in some areas. In one embodiment, manychannels may flow underneath the bottom of the LEDs and very close tothe bottom of the LEDs separated by only about 125 um of copper (range1-1,000 um), plus a thin layer of solder that is used to bond the LEDdirectly to the common anode substrate 317. Additionally,multi-directional etched coolant paths and orientations, individually orin groups, also described as internal heat transfer channels, runningparallel, perpendicular, vertically, or horizontally, connected, or notconnected, or some combination of both, oriented with respect to thelength or width or some combination or both, of the LED array 330,and/or the bottom surface of the LED(s) may be considered.

According to one embodiment, the internal heat transfer channels may beoriented such that (i) two or more adjacent LEDs in the shortestdimension of the LED array have substantially independent heat transferchannels under each LED and (ii) the LEDs above these channels arecooled independently (i.e., the group of channels under each LED havesubstantially no convective communication with each other or with thegroup of channels under the adjacent LED). Hence, the two or moreadjacent LEDs are said to be cooled in thermal parallel rather than inthermal series. Thermal series would result if the channel flowsubstantially directly underneath the LEDs was commingled or if a commonchannel flowed substantially directly underneath both LEDs.

The foil layers (e.g. foil layer 520) of the micro-channel cooler 410are preferably substantially copper, and they preferably have around 1%(range 0.1-10%) of an interspersed ceramic material such as Al₂O₃ andknown commonly as Glidcop, which is known to maintain its stiffness,strength and shape after being subjected to high diffusion bondingtemperatures. Glidcop is now available having nearly the same thermalconductivity as pure copper.

In one embodiment, the micro-channel cooler 410 is constructed as a highaspect ratio device corresponding to the high aspect ratio of thedirectly mounted LED array 330. This is to say that the cooler 410 has alonger length on which the LED array 330 is mounted along, than itswidth, and the cooler 410 itself often has many short channels side byside and with flowing coolant in a direction often parallel to the widthof the LED array 330, and perpendicular to the long-axis of the cooler410 (the largest dimension), and that may have 1-n channels located sideby side to one another. Internal micro-channels may be oriented to formmanifolds that are parallel, perpendicular, horizontal and/or verticalto either or both the long-axis (length) or the short-axis (width) ofLED array 330. The foils (e.g., foil layer 520) are then preferablystacked on top of each other (or together) with each channel preferablylocated underneath the channel that is located on or in the foilimmediately above the neighboring foil whether or not the foils arestacked in any vertical or horizontal or other angular or rotationallylocated orientation in a three dimensional space. In one embodiment, theLED(s) are mounted directly to the surface (e.g., a common anodesubstrate) formed by the edges (when the foils are stacked vertically)of a multiple diffusion bonded stacked foil laminate. It is preferablethat the surface formed by the edges of the foil laminate be first madeflat before LED array 330 is soldered to this surface.

As a non-limiting example, the LEDs could be mounted in two (1-n) rowsacross the width, and be on the order of 50 to 300 LEDs along the lengthof the row. The length of the row is preferably around 90% (10-100%) ormore of the length of the cooler 410. That is the LED array 330 extendsas close as possible to the edge of the micro-channel cooler 410. Inthis manner, there is no significant irradiance gap in seriallyconnected UV LED lamp head modules 200. This configuration is mostbeneficial in the context of short working distances (˜2 mm).

It is preferable that the internal micro-channels running beneath theLEDs of LED array 330 have approximately equal flow so that thejunctions of the LEDs are approximately the same temperature. For somespecialized applications the flow could be different in some channels torun LEDs hotter or cooler, especially if the LEDs are of differingwavelength as short wavelength LEDs may require more cooling. It shouldbe noted that not all embodiments require 100% of the coolant runningthrough the micro-channel cooler to run through heat transfer channelsof the micro-channel cooler.

According to one embodiment, CFD is preferably employed to design themain inlet and outlet coolant manifolds formed in base of the body 305to enhance or constrict coolant flow as needed to accomplish theaforementioned desirable nearly equal flow in the micro-channels. CFD ispreferably conducted by MicroVection USA. Enhancement could beaccomplished by making the channels deeper or wider or both, orconversely, constriction could be accomplished by making the channelsshallower or narrower or both. All of these geometries could be threedimensional with simple or compound contours or nearly straight or sharpgeometries. Again, speaking to the micro-channels, they could be ofdiffering size, shape, depth, width, number, center to center spacing,number of etched foil layers, curves, protrusions, squiggles,gull-wings, etc. needed in order to balance flow and or reduce thermalresistance between the channels and the LED junctions.

FIG. 6 is an exploded magnified isometric cut-away view of a top portionof the body 305 of and illustrating various layers of the UV LED lamphead module 200 of FIG. 2. In this example, LED array package 318includes the dielectric spacer layer 514, the cathode layer 513, thedielectric separator layer 512, the adhesive layer 511 and the commonanode substrate layer 317. Flex-circuit 510 could also include an anodelayer (not shown). As described above, layers 511-514 may collectivelyform a flex-circuit 510 from the Pyralux family of product. In oneembodiment, the flex-circuit 510 may not include the dielectric spacerlayer 514, which could be bonded to a bottom surface of the reflector201 or simply be free floating between the bottom surface of thereflector or bonded to a top surface of the flex-circuit 510. Inalternative embodiments, a rigid flex or rigid circuit with a rigiddielectric (e.g., FR4, ceramic, glass or the like) could replaceflex-circuit 510.

In one embodiment, dielectric spacer layer 514 and dielectric separatorlayer 512 comprises a polyimide (e.g., Kapton, available from DuPont,USA), PEN or PET layer. The cathode layer 513 is preferably a copperfoil. Cathode layer 513 and dielectric separator layer 512 preferablyform an integrated layer of cathode foil and dielectric (which is knownas “adhesiveless” in the Pyralux family of products available fromDuPont, USA). As described above, these layers forming LED package 318are pinched between cathode claws 320 a-d and 321 a-b and anode body 315a-b.

One design choice is binning individual UV LED lamp head modules (whichwhen forming serial arrays would typically require connecting lampswithin the same bin) versus binning LEDs within UV LED lamp headmodules. Having the capability to bin within individual UV LED lamp headmodules means one need not bin individual lamps. As noted above, in oneembodiment in which binning is performed within the UV LED lamp headmodule 200, flex-circuit 510 (e.g., comprising an electrically isolated(segmented) cathode layer 511, dielectric separator layer 512 anddielectric spacer layer 514) is employed to potentially individuallyaddress each LED of the LED array 330, or groups of LEDs so that theLEDs may be binned for Vf, wavelength, size, power, etc. in groups from1-n, thereby substantially lowering the demands on the LEDmanufacturer(s) to supply LEDs in just one or a few bins. According toone embodiment, the bins can be about 0.1Vf or less—and most preferably0.05Vf or less, or even 0.01Vf or less. Depending upon the particularimplementation, the LEDs of LED array 330 could be in just one or twolarge Vf bins, such that one or two long strips of LEDs in the arraysare from the substantially same Vf bin. Conversely, the bins could be astight as 0.00001Vf. In this example, segmentation of the flex-circuitlayer 510 and or the LED driver PCBs 310 a-b could be reduced or eveneliminated. This may be accomplished when very large volumes and orlarge LED chips are produced and there are substantial numbers of LEDsavailable from the manufacturers in Vfs that are close to 0.001 Vf orless.

However, the segmentation of the LED driver PCBs 310 a-b and flexcircuit 510 allows numerous options to bin by Vf values, or not at all.In the present example, the LEDs of LED array 330 are divided into eightindividually addressable groups by locating them within eightflex-circuit segments (four of which are visible in the present view,i.e., segments 611 a-d). In one embodiment the segments 611 a-d areformed by photolithographically patterning the cathode layer 513 andetching away the metal foil to form electrical isolation traces (e.g.,electrical isolation trace 610). Dielectric layer 512 in the area belowthe LEDs is removed by laser machining, routing or stamping.

In general, the most suitable UV LED wavelengths are in the range ofabout 360-420 nm, and most preferably ˜395 nm. It should be noted that amix of wavelengths may be use in each UV LED lamp head module 200 andsmaller groups and/or even individual LEDs or some combination of both,may be individually addressed by wire bonding to an individualconductive stripe (not shown) of cathode layer 513 (patterned conductivecircuit material layer) on flex-circuit 510, the conductive stripe(conductive circuit material layer) being preferablyphotolithographically imaged and etched with a preferably polyimide(non-electrically conductive layer a/k/a dielectric layer) beneath it.The cathode layer 513 is usually copper.

According to one embodiment, separator gasket 314 (e.g., monolithico-ring 420) fits in a groove machined or molded into the body 305. Asdepicted in the present example, the groove (or gland) shape machinedinto the body 305 may be roughly described as an “o” with tight radiusesin the corners and a portion running through the middle of the gasket inthe long axis direction. This preferably single-plane gasket design ismade possible by the unique foil layer design in which the etchedinternal passages of the micro-channel cooler 410 for coolant are foundonly in the portion that lies substantially under the LED array 330, andnot in the portions around the areas that fall substantially under theheat spreader peripheral regions. This allows the bottom of thepreferably monolithic micro-channel cooler assembly to be flat andsubstantially parallel to the mating portion of the lamp body 305 thatcontains the groove for the separator gasket 314.

The peripheral regions of the micro-channel cooler assembly noted aboveare best explained as the regions that substantially exist outside ofthe coolant flow areas and/or the regions that exist under thepreferable “o” cross-section seal. A benefit of this design is thatmultiple seals or a seal with differing z-axis planes is avoided. Inessence, a three-dimensional (z-axis on two or more planes) configuredseal is not needed as a more simple planar two-dimensional (z-axis onone plane) seal will suffice. The diffusion bonded foil layers (e.g.,foil 520) are etched with not only heat transfer passages beforediffusion bonding, but also the primary inlet/outlet micro-channels(e.g., primary outlet micro-channel 411) may be etched in an embodimentof the instant invention. Thus, when the foils 520 making up themicro-channel cooler 410 (e.g., 200 micron thickness) and the foilsmaking up the portion of the micro-channel cooler 410 typically havingno heat transfer passages (e.g., solid capping layer 530 and etchedcapping layer 525) are bonded together, a monolithic micro-channelcooler assembly (including micro-channel cooler 410) results that has aflat bottom side that is used to compress the uniquely shaped seal thatexists between the preferably monolithic micro-channel cooler assemblyand the preferably monolithic lamp body 305.

Not shown is an optional monolithic diffusion bonded heat spreader layer(e.g., approximately 0.5 mm thick (range 0.1 to 1 mm)) that may span thetop surface of common anode substrate 317.

FIG. 7 is a magnified isometric view of a reflector 201 of the UV LEDlamp head module 200 of FIG. 2 with an end cap removed. This view isintended to illustrate the modularity of reflector 201. In this example,two of four screws 715 are shown that affix the reflector 201 to thelamp body 305. By simply removing these screws 715, a new reflector withdifferent optical properties can be substituted in place of reflector201. In the current example, integral injection molded feet (e.g., foot716) may be used as alignment features for mini-reflectors (discussedbelow) or end caps. Steel screws 715 could be used to orient, alignand/or hold such mini-reflectors in place if, for example, themini-reflectors contained magnets (with their magnetic fields orientedproperly with respect to the screws 715).

Also, locating pins or mated male/female features that extend from thebottom of the reflectors into or through the micro-channel cooler 410 aswell as into the lamp body or vice versa may be employed for ease ofalignment of the reflector 201 with respect to LED array 330. These pinsor mating features may be part of the injection molded reflector or partof an injection molded (e.g., inserted molded) lamp body.

In one embodiment, locating pins, such as pin 705, could be used toalign mini-reflectors or end cap reflectors. Screws 710 could be used toaffix end cap reflectors to reflector 201.

Protective housing 202 is shown that preferably injection molded andeach half may be a mirror image of the other.

FIG. 8A conceptually illustrates a cross-section of two macro-reflectors810 a-b and 820 a-b superimposed on top of each other in accordance withan embodiment of the present invention. In this example, themacro-reflectors 810 a-b and 820 a-b have substantially the sameexternal height and width but are optimized for different workingdistances. Having a single deep trough macro reflector length and thenhaving differing internal curved surfaces for differing focuses isefficient from a manufacturing standpoint as only a single outer mold isneeded and differing curves are simply differing mold inserts.

In the present example, macro-reflector 810 a-b is optimized for a 53 mmfocal plane 840 and macro-reflector 820 a-b is optimized for a 2 mmfocal plane 830. Each curved portion shown is a mirror image of theother (assuming they have the same focal length) and represent a portionof a complete ellipse, parabola and/or a combination of the two. Aparabola is a special case of an ellipse and would generally be used forcollimating light.

An ellipse has two focuses, a primary focus and a secondary focus. Inthe current example, the primary focus is in the LED plane 870 and thesecondary focus is in the work piece plane 830 or 840.

In various embodiments of the present invention, marginal ray 811(representing the first ray captured by reflector 810 a) and the lastray (not shown) captured by reflector 810 a and exiting an LED arraydefine an angular extent 850 of approximately between 60 to 89 degreesand preferably 80 to 85 degrees, thereby exemplifying (using asimplistic 2-dimensional analysis) that the 53 mm macro-reflector 810a-b controls more than approximately 80% of the photons that leave theLED array. In fact, 3-dimensional computer analysis suggests such a deeptrough reflector design (when end caps (e.g., end caps 207 a-b) are inplace) controls over 90% of the photons that leave the LED array. Thelarger the angular extent the greater control over the photons that exitthe LEDs. Therefore, angular extent can be increased, but practicalconsiderations for reflector sizes (lengths and widths) need to be takeninto consideration.

With reference to FIG. 8B it can be seen that marginal rays 821 a-b(representing the first ray captured by reflector 820 a and the last raycaptured by reflector 820 a, respectively) exiting LEDs 850 a and 850 band reflecting off reflector 820 a define an angular extent 860 ofapproximately between 65 to 89 degrees and preferably 82 to 87 degrees,thereby exemplifying (using a simplistic 2-dimensional analysis) thatthe 2 mm macro-reflector 820 a-b controls more than 82% of the photonsthat leave the LED array in accordance with an embodiment of the presentinvention. In fact, 3-dimensional computer analysis suggests such a deeptrough reflector design (when end caps (e.g., end caps 207 a-b) are inplace) controls over 96% of the photons that leave the LED array.

FIG. 9 shows a portion of macro-reflector 910 optimized for a 2 mm focalplane 940 in which each side of the reflector has a focal point 920 thatis offset from a centerline 931 of a focused beam 930 (having a totalpattern width of approximately 7 mm and a high irradiance center portionof approximately 0.65 cm) on a work piece (not shown) in accordance withan embodiment of the present invention. As depicted in the drawing, insuch a configuration, reflected light rays from the right-hand sidereflector move from the left of the centerline 931 inward toward thecenter and reflected light rays from the left-hand side reflector movefrom the right of the centerline 931 inward toward the center. In thismanner, the two sets of reflected light rays overlap to create the highirradiance beam 930. Computer modeling indicates about a 10% higherirradiance level than if the two sets of reflected light rays did notoverlap. Notably, in one embodiment, at longer focal planes distances(e.g., ˜53 mm), there is no significant loss (less than 5%) ofirradiance at planes +/−3 mm from the focal point.

FIG. 10 is a graph illustrating estimated convective thermal resistancefor various channel widths. This figure graphically depicts the lineardecrease in thermal resistance with decreasing width of individualmicro-channels. Of note is the fact that embodiments of the presentinvention usually use channels having widths of less than 0.1 mm, andoften 0.05 mm, 0.025 mm or less. In another embodiment, mini-channelsare also considered that may be wider than 0.1 mm up to about 0.5 mm.This is contrasted with the width of channels used in prior art UV LEDlamp devices, such as those manufactured by Phoeseon (USA) andIntegration Technology (UK), which are believed to use macro-channels onthe order of 0.5 mm or larger.

As can be seen from the graph, all else being equal, the order ofmagnitude decrease in thermal resistance from a 0.55 mm channel to a0.025 mm channel would in and of itself result in an order of magnitudedecrease in LED junction temperature. However, all else is not equal. Ascurrently understood by the inventors, the prior art has only onethermally-related factor working in its favor. This factor being the useof a low brightness, low fill-factor (LED packing density) array, whichspreads out the heat sources and results in a low thermal density, whichrequires a correspondingly lower heat transfer coefficient for the samejunction temperature.

Embodiments of the present invention minimize bulk thermal resistanceloss through the copper substrate due to the minimal (usually about 125um (range 5-5,000 um)) thickness between the bottom surface of the LEDsand the heat transfer passages (micro-channels).

FIG. 11 is a graph illustrating output power for various junctiontemperatures. This figure shows the severe drop off in UV LED efficiencywith increasing junction temperature. A drop of inefficiency of 40% isnoted with a junction temperature increase from 20 to 88 degrees C. UVLEDs are much more sensitive to heat than some longer wavelength blueand green LEDs. Hence, it is desirable to use superior thermalmanagement in order to keep the junction temperatures low to achieveboth long life and maintain a reasonable efficiency.

In accordance with embodiments of the present invention, LED junctiontemperatures of approximately 40-45 degrees C. are obtained, even whenoperating at current densities of over 2.5 A/mm², and sometimes over 3A/mm². This may be contrasted with the UV LED lamp heads of Phoseon andIntegration Technology that probably operate at current densities ofless than 1.5 A/mm², with LEDs spaced much further apart (lowfill-factor/low packing density), which of course leads to lower peakirradiance and lower total energy delivered to the work piece.

FIG. 12 is a graph illustrating an irradiance profile for a UV LED lamphead with a reflector optimized for a 2 mm focal plane in accordancewith an embodiment of the present invention. According to the presentexample, maximum (peak) irradiance of approximately 84.8 W/cm² isachieved with an output beam pattern width of approximately 0.65 cm andproducing an average irradiance across the width of the output beampattern of approximately 31.6 W/cm² and total output power ofapproximately 20.5 W per cm of output beam pattern length. This examplewas generated with a computer model assuming the use of SemiLEDs'˜1.07×1.07 mm LEDs, with each LED producing 300 mW output at 350 mA. Itis to be noted that embodiments of the present invention could run eachLED at higher current (e.g., approximately 2.5 A or more) atapproximately 0.75 W to 1.25 W.

FIG. 13 is a graph illustrating an irradiance profile for a UV LED lamphead with a reflector optimized for a 53 mm focal plane in accordancewith an embodiment of the present invention. According to the presentexample, maximum (peak) irradiance of approximately 24 W/cm² is achievedwith an output beam pattern width of approximately 3.65 cm and producingan average irradiance across the width of the output beam pattern ofapproximately 5.9 W/cm² and total output power of approximately 21.7 Wper cm of output beam pattern length. This example was generated with acomputer model assuming the use of SemiLEDs' ˜1.07×1.07 mm LEDs, witheach LED producing 300 mW output at 350 mA. It is to be noted thatembodiments of the present invention could run each LED at highercurrent (e.g., approximately 2.5 A or more) at approximately 0.75 W to1.25 W.

According to one embodiment, in which LED drivers are integrated withinthe UV LED lamp head module, off the shelf AC/DC power supplies designedfor high volume “server farms” may be used. Exemplary front end suppliesare available from Lineage Power USA model CAR2512FP series 2500W powersupplies. Preferable supplies are Power-One LPS100 12V 1100W single fanserver supplies that are highly efficient platinum rated front-end AC/DCpower supplies that have power factor correction, may be in electricalparallel, and have a GUI i2C interface, the Lineage power supplies areavailable with a subsystem that incorporates four of these unitsoff-the-shelf (OTS). In 2011 these Lineage units will be similar butwith conduction cooling (without fans).

According to embodiments of the present invention, in addition tocooling the integrated drivers, the coolant water may also beadvantageously employed to cool these power supplies simply by runningthe coolant line through a heat sink in communication with the elements(or the base plate) of the supply that need cooling. It is optimal toderate these Lineage supplies as they are more efficient at a percentageof their maximum power. By way of a non-limiting example, running eachPCB with ˜15 drivers at ˜40 amps and ˜4-5 volts one would use about 60%of the ˜10000 W available. It is optimal to design for ˜50A or greaterand ˜5.5 V to have some headroom now and into the future when thepreferably ˜16 LEDs that are around ˜1000-1200 um square on each of allfour sides (though they could be of any size and shape such asrectangular, or larger size such as ˜2000 um or ˜4000 um or larger perside) are desired to be operated at a current of ˜3A per LED or ˜48 pergroup solely by way of a non-limiting example. In one embodiment, thecathode bus bars 313 a-b on each PCB 310 a-b near the backside of thelamp body 305 could run nearly the length of the preferably ˜300 mm longboard (not shown) as well as solder pads running nearly the length ofthe PCB. In one embodiment, the cathode cross plate 375 represents a tiebar affixed across cathode bus bars 313 a-b which provides an effectiveattach point for the preferably single main cathode wire 205 going fromthe UV LED lamp head module 200 to the AC/DC power supplies preferablyin somewhat similar fashion to the preferable single main large AWGrange ˜1-10 and preferably ˜2 AWG core anode wire going from thepreferably constant current (CC) DC PCB boards of the UV LED lamp headmodule 200 to the supplies that are preferably connected to the AC mainsto give a highly efficient power source to the LEDs with low ripplepreferably less than 10% to maximize LED lifetime. On the PCB there maybe some shared components of the aforementioned non-limiting example of˜15 CC drivers such that there would not be a definitive requirement for˜15 separate components that may not have to have their cathodesisolated. It should again be noted that 1-n cathode and anode cables mayfeed the lamp with electrical power from 1-n power supplies or mains. Itmay be preferable to use four Lineage USA 2500W power supplies per lampand run them at derated power for efficiency. They are available with acommon back end for ˜4 power supplies. With or without the back end fourseparate anodes and cathode wires/cables per lamp may be considered soas to allow the use of smaller diameter cables (methode/cableco, USA)and or large cables and less resistive losses.

In view of the foregoing, it can be seen that embodiments of the presentinvention are predicated on closely spaced array(s) of LEDs, also knownas high fill-factor arrays, so that maximum brightness can be obtained.This is to say that the optical power per unit area per solid angle ismaximized, as brightness may be roughly defined in the present contextas power per unit area per solid angle. This high brightness alsocorrelates nearly linearly with heat flux/thermal demand as the wasteheat from the electrical to optical power conversion becomes more denseas the array density increases. Embodiments of the present inventionpreferably utilize a fill-factor array of LEDs of equal or greater than90%, but has a range of 30-100%. The application of a high fill-factorarray in accordance with embodiments of the present invention lead to anextremely high and dense heat load on the order of 1000 W/cm² or more,range 100-10,000 W/cm². This high thermal flux is an artifact of thehigh brightness, i.e., the LEDs are in very close (1-1000 um) proximityto each other, operated at currents of 2-3 or more amps per square mm,(range 0.1 to 100 A), which results in extremely high heat flux demands,and of course concomitantly requires extremely low thermal resistancecooling technology that combines both a very high degree of cooling(e.g., convective cooling and/or conductive cooling (e.g., thin and highconductivity layers between the LED and flowing gas or liquid)) toachieve junction temperatures that are preferably as low as 40 C or lessfor long life and efficient operation at extremely high output power.

An alternative embodiment of a UV LED lamp head module 1400 in which theLED array is comprised of multiple groups of seriesed LEDs connected inelectrical parallel is now described with reference to FIGS. 14A-D. FIG.14A is an isometric view of UV LED lamp head module 1400 in accordancewith an alternative embodiment of the present invention. FIG. 14B is aside-facing, exploded view of the UV LED lamp head module 1400 of FIG.14A, depicting the unassembled components of the lamp head module 1400subsystems and their respective components. FIG. 14C is a rear-facing,exploded isometric view of the UV LED lamp head module of FIG. 14A,depicting the rear connections. FIG. 14D is an exploded view of flexcircuit subsystem 1450 and cooling subsystem 1470 in accordance with anembodiment of the present invention.

In the present example, lamp head module 1400 includes a reflectorsubsystem 1460, a flex circuit subsystem and light emitting subsystem1450 and a cooling subsystem 1470. These subsystems work together toemit UV light intended for use as a curing (e.g., photochemical curing)mechanism for materials such as, but not limited to, paints, coatings,inks, adhesives, laminates and the like. Cooling subsystem 1470,including a micro-channel cooler 1401 and lamp body 1404, is intended tocool light emitting elements, e.g., an array of LEDs, laser diodes orthe like 1407 of the light emitting subsystem allowing for high powerdensity light output. Cooling system 1470 may also include a means(e.g., mounting interface 1475) for mounting lamp head module 1400 ormultiple lamp head modules (not shown) to an external device, such as anexternal frame, stand or track. Such track provides the means for thelamp head module(s) to be integrated into a manufacturing, printing orother process.

Reflector subsystem 1460 consists of a pair of reflectors 1418, a pairof reflector end caps 1417, an optical window 1421 and a magnetic windowmount 1424. Reflectors 1418 may be bonded to reflector end caps 1417 byscrews 1427 to form an internal reflective chamber (not shown), whichworks to focus light (preferably, according to non-imaging physicalprinciples) emitted by the light emitting subsystem. The interiorsurfaces (not shown) of the internal reflective chamber are highlyreflective. According to one embodiment, high reflectivity is achievedthrough a combination of polishing and coating of the interior surfaces.

Window 1421 is placed at the top of the reflective chamber and is fixedin place by window mount 1422 and an array of magnets or screws 1423.

Reflector subsystem 1460 is attached to cooling subsystem 1470 with theflex circuit subsystem 1450 interposed there between by a series oflocating pins 30 and fixed in place by mounting screws. Optionally, aspacer layer (not shown—see FIG. 16B) may be placed immediately belowthe reflector subsystem 1460 to provide adjustment (e.g., z-heightadjustment) and aid in the assembly process.

A main outlet lamp body cooling fluid channel 1461/1462 and a main inletlamp body cooling fluid channel 1461/1462 are formed within lamp body ofthe cooling subsystem 1470.

Micro-channel cooler 1401 is recessed in pocket 1434 of lamp body 1404.This recessed pocket 1434 allows the flex circuit 1403 (that may bebonded to the top of micro-channel cooler 1401 and extends over one ormore sides of the micro-channel cooler 1401) to be smoothly bent aroundan edge 1435 of lamp body 1404. Micro-channel cooler 1401 may beconstructed as described above with reference to FIGS. 4A-C and FIGS.5A-B; however, in the context of the present example, micro-channelcooler 1401 does not need to be conductive. As described above,micro-channel coolers meeting the cooling requirements described hereinare available from Micro-Cooling Concepts of Huntington Beach, Calif.

As described in further detail below, in one embodiment, flex circuit1403 is a multi-conductor flex circuit that preferably contains twoconductors with opposite polarity. Flex circuit 1403 has a high aspectratio in relation to its length along the long axis of LED array 1401 tothe height of the LED array/submount combination. This allows a largeamount of electrical current to flow to LED array 1407 in a compact zheight thickness stack up. The stack up of the LED/submount is nearlythe same as the flex circuit stack (as illustrated in FIG. 16B) and anoptional free floating unattached spacer layer that makes up anyz-height difference or intentionally adds to the z-height difference andestablishes a base for the bottom of reflector subsystem 1460.

In the example depicted, an elongate opening 1440 (e.g., a void, awindow, a gap, a hole or an aperture) in flex circuit 1403 serves a dualpurpose of getting anode and cathode bond pads close to the LEDs andsubmount 1406 with low thickness (height), but may also serve as amechanical guide when the submount 1406 is soldered into position.Indium Corp. of America, USA, provides both the flux (e.g., WS-3622) andthe Indium containing preforms may have approximately 3% silver forbetter wetting and preform rigidity. The elongate opening 1440 may berectangular or any other geometric shape.

In the depicted embodiment, flex-circuit 1403 is essentially formed overedge 1435 and the flow of electrical current in flex-circuit 1403 isessentially redirected from a plane that is substantially parallel tothe p-n junction plane of LED array 1407 to a direction that issubstantially perpendicular to the p-n junction plane. Flex-circuit 1403fits under reflector subsystem 1460 and is further held in position bycover 1415. Zener diodes (e.g., zener diode 1402 available from LittelFuse, Inc., USA) are shown in pockets (e.g., pocket 1436) formed withinflex-circuit 1403 and are soldered into place and connected to a cathodelayer of flex-circuit 1403 by a plated through hole in accordance withconventional surface mount technology (SMT) manufacturing technology. Asdescribed above, lamp body 1404 may be machined or injected molded orsome combination.

Flex circuit subsystem 1450 is connected to cooling subsystem 1470 byhardware 1426. According to one embodiment, a fluid-tight seal isproduced between a micro-channel cooler 1401 and a lamp body 1404 oflamp head module 1400 by use of a custom-shaped o-ring 1405 availablefrom Apple Rubber Products of Lancaster, N.Y. Pins 1428 locate thereflector subsystem 1460 to the cooler subsystem 1470.

In the present example, lamp body 1404 provides both the fluid coolingpaths for inlet and return as well as the mechanical structure to mateand fix all the subsystems together. Cooling fluid enters lamp body 1404from an input tube 1420 connected to lamp body 1404 by an inlet tubeclamp 1432 and its associated hardware 1431. Fluid flows from the inletplenum of the fluid body through the micro-channel cooler 1401 where itbecomes calorically warmed by the waste heat generated by LED array1407. This warmed fluid then travels through an exhaust plenum(typically of identical geometry) to an outlet plenum where it is thenreturned to a cooling means (not shown) (e.g., a chiller, heat exchangeror the like) via an output tube. Output tube may be affixed to lamp body1404 in much the same way as the inlet side but uses a differentlyconfigured (e.g., keyed) clamp 1416.

A cover 1415 is mounted to lamp body 1404 with hardware 1424. Cover 1415covers and protects flex circuit 1403 and wire connectors of flexcircuit subsystem 1450. Cover 1415 also holds the shape of the flexcircuit 1403.

In one embodiment, lamp body 1404 has an integral protrusion (e.g.,inlet clamp 1432) that inlet hose 1420 is pushed over. Similarconnectivity may be provided for the outlet hose. Preferably captiveand/or keyed machined hose clamps (e.g., 1432) are employed. The keyedlocation prevents unwanted rotation of the hose clamps and the captivefeature makes installing hoses far less cumbersome. The hose clamps maypreferably have “t” shaped slots, which may be wire electro-dischargemachined (EDM) with preferably 120-degree separation for more uniformhose clamping action.

Cathode electrode 1413 and anode electrode 1412 are shown in FIG. 14D.These electrodes clamp or sandwich the flex-circuit 1403 betweenthemselves and the lamp body 1404. Under each electrode are exposedareas of either the flex-circuit anode layer or the flex-circuit cathodelayer so as to effect electrical contact and continuity between therespective electrode and flex-circuit surfaces.

In the context of the present example, flex circuit subsystem 1450preferably includes a high-density array of LEDs 1407, a multi-layer,multi-conductor flexible circuit 1403, a micro-channel cooler 1401, anelectrostatic discharge (ESD) protection device 1402, a power supplycable 1421 and a power return cable 1422. The cables are attached withtheir respective electrodes (e.g., mounting blocks) 1412 and 1413. Thesemounting blocks connect each cable to their respective conductor layerin flex circuit 1403. This enables electrical power to travel from aremote power source (not shown) to lamp head module 1400 via the powercables 1419 and 1420 and to the LED array 1407 through flex circuit1403.

According to one embodiment and as described in further detail below,LED array 1407 is made up of multiple (e.g., three) smaller arrays ofseriesed LEDs arrays placed in parallel, each of the multiple smallerarrays (each a “group”) include multiple (e.g., twelve) LEDs. In oneembodiment, these smaller arrays are constructed by solder andwire-bonding the LEDs to a submount 1406.

LEDs are arrayed along the submount 1406 in the long direction to formLED array 1407. The last edge of the first LED proceeds the beginningedge of the next LED, and so on (e.g., placed edge-to-edge). In oneembodiment, between any two LEDs there is no intervening metalizationand/or bond pad or circuit trace material. This allows the LEDs to beplaced as closely as possible to each other thereby maximizing lightemitting area in the long direction of LED array 1407 by minimizing deadspace between LEDs. If there was elongate bonds pads, wire bond padarea, and/or circuit trace metalization between the LEDs, then the LEDswould have to be placed further apart, which would compromise the lightemitting area along the long direction of the LED array 1407. In oneembodiment, maximizing light emitting surface in the smallestarea—length×width—is desired. Furthermore, a high aspect ratio—lengthlonger than width—is also employed by the elongate reflector halves/clamshell—to control the emitted photons in a pattern on the workpiece thatis preferably the same geometric shape as the emitting area with thegoal of eliminating scattered photons around the edges (a/k/a blur).

In various embodiments and as described in further detail below, theremay be three distinct wire-bond connections for each group of LED array1407. For example, wire-bond connections (e.g., wire-bond 1708) may bemade between the positive power path layer, also known as supply oranode, of flex circuit 1403 and anode pads of a first LED in a group. Asecond wire-bond type (e.g., wire-bond 1709) occurs from each LED in agroup (with the exception of the final LED of the group), which bondsthe LED cathode pad to a stem on submount 1406 electrically connectingit to the anode of the next LED in the group. The cathode pads of thefinal LED are connected to the cathode or return layer of flex circuit1403 by a third type of wire-bond (not shown—see wire-bond 1710 of FIG.16C). Wire-bonds 1708, 1709 and 1710 are shown in greater detail in FIG.16C and FIG. 17D-F.

In accordance with one embodiment, the multiple groups of seriesed LEDsare placed in a line, edge to edge to produce a high-density array. Inone embodiment, electrically, LED array 1407 is an array of multiple(e.g., three) parallel paths each containing multiple (e.g., twelve)LEDs wired in series.

According to one embodiment, submount 1406 is bonded to micro-channelcooler 1401 using a thin solder preform 1410 (approximately 20 micronsor less) to minimize thermal resistance between the LEDs and coolingfluid, which flows through micro-channel cooler 1401.

According to one embodiment, LED array 1407 is comprised of 3 groups of12 80 mil×80 mil LEDs available from SemiLEDs, Taiwan wired inelectrical series. The three groups are wired in electrical parallel.Depending upon the particular implementation, more or fewer paralleledgroups can be used and each of the groups of seriesed LEDs may alsocomprise more of less than 12 seriesed LEDs. The individual LEDs of LEDarray 1407 may be the large chip variety, which are approximately 2019um (80 mil) on each side and 145 um thick. In one embodiment, a UV lightemitting thin film material, e.g., GaN, may be deposited on native GaNsubstrates available from Inlustra Technologies, Inc. of Santa Barbara,Calif. This would enable extreme current densities, e.g., 3+amp/mm² ofLED chip area, with little to no current droop that is common to GaNthin film devices deposited on foreign substrates, e.g., sapphire, SiC.Among other enabling reasons for the extreme current densities is thenear perfect lattice match between GaN and GaN and the high thermalconductivity of GaN. Such extreme current densities generate extremeheat fluxes, which are best managed and/or ameliorated by using amicro-channel cooler as described in the context of various embodimentsdescribed herein.

According to one embodiment, the aspect ratio of the length to width ofthe LED array 1407 is preferably 1:36, but the range may be 1:5-1:1,000.

The preferably 12 seriesed LEDs (range could be 1-100) shown on eachsubmount (e.g., submount 1406). The groups of parallel LEDs could bebinned so that each group all have about the same impedance to reducedeleterious current hogging effects. Load balancing resistors are yetanother means for accomplishing impedance matching so as to (againreduce the chance of a current hogging group), but pre-binning perhapsis considerably more elegant and cost effective. An off the shelf powersupply from GE/Lineage, CP200, Plano, Tex. is the preferable AC-DC powersupply (also known as a rectifier) used to power the UV LED lamp of thecurrent embodiment. The power supply is presently available as a 2000 or2700 W unit with ˜97% efficiency. It also has a very compact form factorand has an extremely rare large output voltage swing. This large outputvoltage swing allows the 3 groups of 12 LEDs to be varied from 100% fullpower of approximately 3 A/mm² LED current density and down to a levelthat is perhaps 0-75% of full power by just using a 0-5V input control.Hence no heavy, expensive, and inefficient DC-DC converters are requiredand one can rely on the full efficiency of the compact, long life (2MHr.MTBF) power supply (rectifier) available from GE.

Submount 1406 is now described with reference to FIGS. 15A-D. FIG. 15Ais a top view of a submount 1406 in accordance with an embodiment of thepresent invention. FIG. 15B is an isometric view of the submount of FIG.15A, showing raised high current carrying electro-deposited features ofthe top surface of submount 1406. FIG. 15C is an edge view of submount1406 of FIG. 15A, which illustrates various layers of submount 1406 inaccordance with an embodiment of the present invention. FIG. 15D is anenlarged view of section D of FIG. 15A, illustrating the uniqueinterlocking geometric configuration of bond pads 1511 and 1512 for twointermediate LEDs in a group of a seriesed LED array. For accuracy andclarity solder barrier 1530 is shown, but it is the very top most layerand electrical current flows underneath it. While for brevity only asingle submount may be described below, it is to be understood thatmultiple submounts (e.g., 3) may be connected in electrical parallel inaccordance with embodiments of the present invention.

According to one embodiment, submount 1406 has two primary functions:(i) to provide a means for electrically connecting one LED within aseriesed group to the next LED within the seriesed group and to flexcircuit 1403 at the beginning and end of each group (the flex circuit1403 connections are shown in greater detail in FIG. 17F); and (ii) toprovide a spacially precise geometric mount for the LEDs that serves tolocate and form them into a high-aspect ratio linear array.

LEDs of LED array 1407 are soldered to an about 5 micro inch gold layeron a bond pad portion (e.g., bond pad portion 1511) of submount 1406.Those skilled in the art will recognize various other means of affixingthe LEDs to the bond pad are possible. For example, epoxy of diffusionbonding may be used to affix the LEDs.

According to one embodiment, the solder used is a SnCu deposited on thebottom surface of the LED. Alternatively, a paste available from IndiumCorp. of America may be used, which may use a flux carrier (e.g.,WS-3622) to attach the LEDs. In yet another embodiment, solder preformsmay be used.

Returning to the present example, underneath the thin gold below bondpad area 1511 (and as described further below with reference to FIG.15C) is a Ni diffusion barrier and Ti adhesion layer. Finally, there isa thick (e.g., 1 to 2 mil) copper current conduction layer forming aninterlocking L-shaped structure (e.g., 1510 and 1520), a thick “arm”portion of which (e.g., 1511 and 1521) extends completely below thesoldered portion of the LED and extends around to form a current trace(e.g., 1513 and 1523) and a wire bond pad area (e.g., 1512 and 1522),which together represent a “stem” of their respective L-shapedstructures 1510 and 1520. In one embodiment, submount 1406 includesmultiple alternating L-shaped structures in opposing orientation. TheL-shaped patterned circuit material layers may be pattered on thesubmount in an inter-locking arrangement in which the stem portion ofadjacent L-shaped patterned circuit material layers of the plurality ofL-shaped patterned circuit material layers are located on opposite sidesof the array and run substantially parallel to each other.

Since stem portion 1512 of L-shaped copper current conduction layer 1510operates as a wire bond area, in order for reliable wire bonds to form,it is desirable to have thicker 125 micro inch gold. Also, it isdesirable to avoid solder creep or flow onto bond pad areas (e.g., 1511and 1521). Hence, in one embodiment, a solder dam or solder barrier(e.g., solder barrier 1530) is effectuated from the square edge of bondpad 1511 at the beginning of the elongate portion and extending about 2mils towards the wire pad trace region. This solder dam is preferablyTiW that is sputtered through a mask onto the wafer before the surmountsare diced into individual chips. This solder dam functions because TiWreadily oxidize in air and solder will not flow across an oxidizedsurface.

Although bond pad (e.g., 1511), circuit trace (e.g., 1513), and wirebond pad area (e.g., 1512) all essentially share the same monolithicconductive current carrying layer, which is essentially the samegeometric shape described by an “L”, the bond pad area can still beconsidered elongate as it extends beyond the area that is substantiallyunderneath the LED. This elongate shape is orthogonal to the long axisof the LED array 1407, as well as the array of submounts that arethemselves arrayed edge to edge in an elongate pattern.

Circuit trace (e.g., 1513) is elongate along the long axis of LED array1407 as it not only traverses the gap between the last edge and thebeginning edge of each LED in the array, but also traverses the distancebetween the last edge and the beginning edge thereby it is longer thanan LED edge. This elongate portion of the circuit trace is the long thin“stem” of the “L” shape. The length of individual circuit traces, (e.g.,circuit trace 1513) which includes the distance between the LED edgesplus the length of an LED edge itself is preferably an approximate ratioof 8:1, with a range of 4:1 to 16:1. Circuit traces preferably have athickness (including all layers whether adhesion, current carrying, orprotective) that is preferably 50 microns (2 mil thick) with a range ofapproximately 10 to 100 microns and a width that is preferably at least250 microns (10 mil) wide with a range of 50 to 500 microns. In oneembodiment, the cross-section is about 5:1, but could range from 2:1 to20:1.

Since embodiments of the present invention involve a high current fluxdevice, sufficient conductive material (e.g., copper) is typically usedto carry electrical current without undue resistive losses. In aconventional series circuit layout, electrical current from one LED tothe next is often carried through small wires that are conventionallybonded to the top surface of one LED and then to an extended (orelongate) bond pad of the next LED—with the bond pad in electricalcommunication with the bottom surface of this next die. As statedpreviously, this type of conventional series circuit layout could takeup an undesirable amount of area that does not emit photons (non-lightemitting area) along the length of the elongate array. Therefore, in oneembodiment, instead of using wires to carry the current between LEDs, acircuit trace parallel to the outside edge (see, e.g., 1801 of FIG. 18C)of the LED array 1407 is used.

According to one embodiment, submount 1406 consists of a substratematerial (e.g., beryllium oxide (BeO)). In one embodiment, this layer iskept as thin as is reasonably possible in order to minimize the thermalresistance while still maintaining manufacturability. In the presentexample, the bottom surface of the BeO wafer may consist of threelayers: (i) a titanium adhesion layer 1506 b, a nickel barrier 1504 b toprevent absorption and diffusion of a gold flashing 1502 b to provide abondable surface. These layers allow solder to bond to the gold layerand to micro-channel cooler 1401.

The top surface of the wafer has another isolation barrier with a copperlayer 1505 on top. Copper layer 1505 behaves much the same way as acopper etch on a traditional printed circuit board, providing electricaltraces and forming pads on which components may be mounted. In oneembodiment, the thickness of copper layer 1505 is selected to maximizethermal conductivity and minimize electrical resistance whilemaintaining a reasonable manufacturing cost. The top surface of copperlayer 1505 is coated with nickel barrier 1504 a to prevent diffusion ofthe above gold coatings. In the areas where solder 1699 is applied and aSMT component, in this case, an anode pad of the LED, a thin goldflashing 1502 a may be applied. In areas where wire-bonds are to beconnected, a thicker gold pad 1501 may be applied. In areas where solderis not desired an insulation or solder stop layer 1503 of TiW ispresent. In one embodiment, solder stop layer 1503 is used as a “solderdam.” The solder stop layer 1503 also helps to ensure the LEDs remaincentered on the bond pads and do not float during the soldering processwhile maintaining electrical continuity to other pads through the copperlayer 1505 below. In this manner, all top layers may be formed to createmultiple (e.g., twelve) electrically isolated sections—one for each LEDin the group.

In one embodiment, in order to maintain electrically continuity betweenthe bond pad and the circuit trace regions they are of monolithicconstruction. This construction may be manufactured via aphotolithographic process on the native submount wafer that ispreferably BeO or selected from the group of materials that arepreferably both thermally conductive and electrically insulating, e.g.,AlN, diamond, silicon, GaN and the like.

In the context of the present example, a first seed layer of metal maybe sputtered by conventional sputtering means through a mask that hasthe inter-locking “L” shaped pattern that is found repeating down thelong axis of the submount 1406. This pattern is built up through anelectro-plating process. A highly electrically conductive metal, e.g.,copper, is preferred. The seed layer may have an adhesion layer, e.g.,titanium 1506, sputtered firstly. After the thick, preferably copperlayer is electro-plated, a diffusion layer 1504 a, e.g., nickel, isdeposited either by sputtering or electro-plating means. Finally, aprotective layer 1501 may be deposited by sputter or electro-platingmeans. This protective layer is usually a sputtered precious metal,e.g., silver or gold. These metals are usually employed because wiresare conventionally and easily bonded to this protective layer 1501. Thisprotective layer also prevents oxidation of the current carrying layer1505. A solder dam (or solder barrier) (e.g., solder barrier 1503) layeris provided in one embodiment of the present invention. It separatesbond pad region 1511 from the circuit trace/wire bond region 1513 andprevents solder 1699 from under the die (on top of the bond pad) frommigrating into or onto the region where wire bonds may be affixed (thewire bond pad region). Solder in this region would have a deleteriousaffect on wire bond reliability. Solder dam (e.g., solder dam 1503) ispreferably deposited through a mask by sputtering means and ispreferably a highly oxidative material, e.g., TiW.

In the context of FIG. 15D, two exemplary electrically isolated L-shapedstructures are shaded 1510 and 1520. Each of the shaded L-shapedstructures 1510 and 1520 denote the electrically connected layout of onearm (bond pad) and stem combination. A solder dam (e.g., solder dam1530). This unique geometry allows LEDs to be placed in an array with anabsolute minimum of space between them. This density allows for anexceptional power output to be attained with a minimum of space. It alsoallows for heat to be efficiently removed from the LEDs with a minimumof space used.

As described above, solder barrier 1530 between bond pad area 1511 andwire bond/circuit trace area 1513 prevents solder between the bond padand the LED from spreading onto the wire bond area 1513 andcontaminating the surface, which could interfere with wire bonding. Thesolder dam 1530 is preferably deposited by sputtering a highlyoxidizable metal or metal combination, e.g., TiW. The TiW will oxidizereadily and thereby prevent any solder from spreading over it. Dependingupon the particular implementation, the thickness of the TiW may be onthe order of angstroms or nanometers.

Flex circuit 1403 is now described with reference to FIGS. 16A-C. FIG.16A is a top view of flex circuit 1403 of FIG. 14B. FIG. 16B is anisometric exploded view of flex circuit 1403 of FIG. 14B, illustratingthe vertical construction of a flex circuit stack and its position andorientation to the micro-channel cooler 1401 in accordance with anembodiment of the present invention. FIG. 16C is a cross section of theflex circuit 1403 of FIG. 14B, which illustrates the various layers ofthe stack once assembled.

In the present example, flex circuit 1403 is a multilayer flexibleassembly consisting of two isolated electrical layers and associatedpolyamide isolation layers and adhesive layers. An anode pad 1601 ispresent on the top edge of flex circuit 1403, as is a cathode pad 1602.These pad areas provide the respective wire mounts for a firm electricalcontact area to appropriate copper conductive layer by, for example,removing the material of all above layers from the stack in the desiredregion. Material may be removed in the same fashion from the area abovea series of three anode wire-bond pads 1603 and cathode wire-bond pads1604. These exposed copper areas may be nickel barrier coated and goldflashed in order to provide a bondable surface. In one embodiment, flexcircuit 1403 also provides a mounting area 1605 and pair of bond padsfor ESD protection. In the illustrated configuration, six such areas arepresent. Each area has a cathode and anode pad and is located on theupper conductive layer. The other layer is connected to a pad that isisolated from the rest of the layer by a captive plated through-holevia.

According to the present example, the center of flex circuit 1403consists of an electrically insulating polyamide core 1615 made out of adielectric material, e.g., Kapton available from Dupont in Wilmington,Del. In one embodiment, a copper layer is additively grown on the bottomof this core and forms a cathode conductor layer 1614. The same processcan be applied to the top of the core and this layer forms an anodeconductor layer 1616. Copper thickness may vary, but should be as thickas possible to maximize current carrying capacity while stillmaintaining an appropriate bend radius to accommodate the geometricconstraints of the lamp head module as a whole. All other layers shouldideally be kept at a minimally manufacturable thickness so as to notfurther reduce flexibility of flex circuit 1403.

In the context of the present example, an adhesive layer 1617 is placedon the top of the surface of anode layer 1616. Its purpose is to allow apolyamide protective coverlay 1618 on the top surface of the flex stack.These two layers are removed in areas where access to the anodeconductor is desired as shown in FIG. 16A. The same process is appliedto the exposed surface of the cathode conductor layer with an adhesivelayer 1613 and coverlay 1612.

An adhesive layer 1610 that is roughly the dimensions of micro-channelcooler 1401 may be applied to bond micro-channel cooler 1401 to flexcircuit 1403 during a final lamination process.

With reference to FIG. 16C, it should be noted that if the macroreflector is set too high above the emitting layer of the LEDs outputefficiency will suffer as photons will impinge on the bottom surface ofthe reflector without entering the macro-reflector inlet aperture.Efficient capture of photons emitted by an LED by a reflector is knownas capture efficiency. Photons that impinge on the bottom side of thereflector will be wasted and they will simply warm up the reflector anddo no work on the workpiece. On the other hand, if the macro-reflectoris set too close to the emitting surface of the LEDs there is a chancethat it could touch the wires and create shorting, ESD, or lifetimeissues. As such, in one embodiment, the base of the reflector ispositioned at a precise, desired distance from the emitting surface ofthe LED array 1407 using a spacer layer 1611. According to oneembodiment, the entrance aperture of the reflector pair is positionedwithin 0 to 25 microns (range 0-250 microns) above or below the lightemitting surface of the LED array 1407. Note that in the presentexample, the spacer layer 1611 does not extend as far as the otherlayers so as to not unnecessarily add thickness to the bend region,which would make the bending of the flex circuit 1403 around the edge ofthe lamp body more difficult.

Although in the present example, flex-circuit 1403 is shown as wrappingaround one side of lamp body 1404, in alternative embodiments, one orboth of the anode and cathode layers could wrap around both sides andthe anode and cathode layers could be continuous between both sides orhave an electrical discontinuity between both sides.

With reference to FIGS. 17A-17F, novel characteristics of LED array 1407will now be described. FIG. 17A is an isometric view of the LED arrayassembled to the flex circuit and the micro-channel cooler in accordancewith an embodiment of the present invention. FIG. 17B is a top view ofthe LED array of FIG. 17A. FIG. 17C is an enlarged view of section A ofFIG. 17A showing wire-bond connections for a group of seriesed LEDs ofthe LED array of FIG. 17B. FIG. 17D is a further enlarged view ofsection AA of FIG. 17B showing a first LED of the group of seriesedLEDs.

In the context of the present example, each LED or package isconstructed with an anode pad 1701 on the underside of the LED orpackage for SMT soldering and placement. Cathode pads 1702 (shown inFIG. 17E) are located on the top surface towards a common edge of theLED. Cathode pads 1702 are designed for preferably the balls ofwire-bonds to be affixed. Specifically, the foot or wedge end of awire-bond attached as terminating a wire-bond on the LED surface wouldrequire too much downward pressure and damage the LED epitaxial layer.Anode foot 1799 of wire 1709 is affixed to the stem of anode traceforming (where the trace forms a wire bod pad). These two pads providethe electrical connections for the LEDs. An alternating orientation ofthe LEDs is illustrated by FIG. 17B. The alternating orientationfacilitates formation of a high-density array because it allows forseries configuration with a minimal of electrical resistance betweenLEDs as opposed to prior art configurations.

FIG. 17C is an enlarged view of section A of FIG. 17A showing wire-bondconnections for one submount and the beginning of the next submount,which is connected in electrical parallel with the first. An ESDprotection device, in this case a SMT zener diode is also shown.

FIG. 17D is a further enlarged view of section AA of FIG. 17B showing afirst LED in a group of seriesed LEDs and the anode-to-flex-circuit wirebonds (e.g., wire bond 1708) with the ball originating at the submountand the tail connected to anode pad 1603 of flex circuit 1403.

FIG. 17E is a further enlarged view of section AB of FIG. 17B showing anintermediate LED of a group of seriesed LEDs and LED cathode pad 1702 tosubmount wire-bond 1709. In one embodiment, there are four such cathodepads 1702 and wire-bonds per LED.

FIG. 17F is a further enlarged view of section AC of FIG. 17B showing afinal LED in a group of seriesed LEDs. ExemplaryLED-cathode-pad-to-flex-cathode-pad wire-bonds (e.g., wire bond 1710)are shown. In one embodiment, these are the longest wire bonds in thesystem. Care should be taken to minimize their length to prevent unduevoltage drop. Multiple wires to a single pad may be considered as wellas rectangular or other geometric shapes and materials such as copper,silver, gold and the like. The initiating LED and its respective bondsof the next LED submount are also shown.

According to one embodiment, lamp head module 1400 has three submountarrays. By sharing the anode layer and cathode layer provided by flexcircuit 1403, multiple submounts may be wired in parallel. In thecontext of the present example, this produces a final electricalassembly of the three parallel arrays (range 2 to 20) of 12 (range 2 to200) seriesed LEDs.

All wire bonds may consist of a single or multiple wires. These wiresmay be mounted linearly (as shown) or in a stacked configuration.Diameter of the wire may be varied as needed to attain the currentcapacity desired for the specific application. Larger loops may berequired for larger diameters; therefore, it may be advisable to usemultiple smaller diameter bonds in applications with tight mechanicalconstraints.

FIG. 18A conceptually illustrates a power path of a group of seriesedLEDs in accordance with an embodiment of the present invention. FIG. 18Bis a magnified view of the first 4 LEDs of the group of seriesed LEDs ofFIG. 18A. FIG. 18C is a cross section of the group of seriesed LEDs ofFIG. 18A taken along section line A. In FIG. 18A, three of the L-shapedstructures described with reference to FIG. 15D are shaded. FIG. 18D isthe same as FIG. 18A, but excludes the shading of the exemplary L-shapedstructures.

According to the present example, current travels in series from ananode layer of flex circuit 1403 through wire bonds to a wire bond padof the submount 1406, which is connected to the anode pad of the firstLED on the underside of the LED. FIG. 18C shows a cross section of afirst LED in the series. The current path travels through the wire-bondto the submount through the LED where a large portion of the electricalenergy is converted into light energy. Waste heat energy is alsoproduced as a byproduct. The cooler the LED p-n junction is, the moreefficient it is in its light emission. The intent of the coolingsubsystem 1470 is to cool the LED array 1407 while be operated atsubstantial current levels and still maintaining a junction temperaturelow enough to give reasonably efficient operation of the LED array 1407.Power then travels from the cathode of the LED to the stem and bond padof the next “L” of the submount through the wire-bond 1709. This patterncontinues until the end of the group of seriesed LEDs is reached.

FIG. 18A shows how the above described process is repeated in a zigzagpattern until the final LED in the series is reached at which pointwire-bonds of type 1710 are used instead of wire bonds of type 1709 toconnect the cathode pads of the final LED to cathode layer 1604 of flexcircuit 1403 as illustrated in the context of FIGS. 17A-F. It isimportant to note that while the present example uses twelve LEDs inseries, longer or shorter series groups may be employed depending on theapplication. Likewise the LED array 1407 may consist of a singlesubmount or numerous submounts and is only limited by the currentcarrying capacity of flex circuit 1403 and the micro-channel cooler'sability to transfer heat away from the LED array 1407 and maintainacceptable junction temperatures.

FIG. 19 illustrates irradiance patterns from an exemplary 80 mm longreflector that creates an approximately 25 mm wide irradiated areafocused 65 mm below the reflector window 1910 in accordance with anembodiment of the present invention. The planes 1930 a-i showing theirradiance patterns 1920 a-i go from 25 mm to 65 mm below the reflectorin 5 mm increments. The trend in the irradiance patterns at thedifferent depths is that they get narrower as they get closer to thereflector, however since the focal distance of this reflector design isrelatively far away (65 mm), the irradiance pattern widths don'tsignificantly change from the lower to the upper part of the lightfield. So this means that the desired beam width stays relativelyconstant over an increased “depth of field” at this focal distance andthis effect increases as the focal plane distance increases. Accordingto one embodiment, during operation, the distance from the exit apertureto the surface of the workpiece is approximately between 0.01 to 0.1(range 0.01 to 10) times the length of the reflector (i.e., distancefrom the entrance aperture to the exit aperture).

The core of embodiments of the present invention is a high density LEDarray (e.g., LED array 1407), which results in the smallest possibleradiant area with the highest possible radiance (“brightness”). Thishigh density radiant source, made possible due to a very low thermalresistance substrate design (e.g., micro-channel cooler 1401) thateffectively mitigates the high heat density, allows for precise opticalcontrol in the smallest possible sized reflector system. The highdensity radiant source also allows for a reflector with a high captureefficiency. In other words, a high percentage of the radiant energyemitted from the source can be captured and controlled by the reflector.As a result of this increased level of optical control, one desiredirradiance pattern that can be achieved is referred to as the “top hat”pattern. A “top hat” irradiance pattern is one in which higherirradiance values are uniform over some distance with abrupt boundarieson either side as the irradiance decreases to lower or negligiblevalues. This is in comparison to a typical Gaussian, or smoothly taperedpattern, where the irradiance falls off from a center peak value moresmoothly. Such irradiance patterns can be favorable to practicalindustrial applications, such as UV curing. In this particular example,the high density radiant area has been configured into a high aspectratio line source, so the top hat distribution is formed perpendicularto the length of the reflector. Other aspects of the irradiance pattern,such as larger working distances, greater pattern depth of field,increased uniformity and decreased underutilized spill light are alldesirable and all more achievable with the high density radiant sourcedue to the improved optical control it provides.

Embodiments of the present invention create a top hat profile by shapingthe macro reflector profile in a shape that closely approximates orrepresents multiple (e.g., 5,6,7, . . . 10) elliptical profiles on eachreflector half (e.g., 1901 a and 1901 b) in a linear trough. Accordingto one embodiment, the macro reflector profile is optimally designedusing Photopia, a non-imaging ray trace software package available fromLTI Optics of Westminster, Colo. USA. These profiles can be defined inone or more mathematical equations, if so desired.

Each ellipse manipulates or controls the photons that impinge upon itand deflects (reflects) them in such a way as to ultimately “push” morephotons from the center of the pattern on the workpiece to the edges ofthe pattern on workpiece. This can be advantageous to photo curing ofpolymers for a multitude of reasons. An irradiance pattern at largeworking distances allows longer times between output window cleaning aswell as less susceptibility to window damage. Increased uniformity alsoallows better utilization of photons towards the goal of not overirradiating (wasteful) or under irradiating (under curing) any part ofthe workpiece. An irradiance pattern with a greater depth of field isbeneficial when curing 3D objects that require curing on surfaces at arange of distances from the output window. A real-world example of sucha 3D object is curing of ink on beer or soda cans.

FIG. 20 is a graph illustrating cross sections of various irradianceprofiles at a center of a workpiece surface for 5 mm, 25 mm and 50 mmstand-off distances (i.e., the distance between the window of themacro-reflector and the surface of the workpiece) in accordance with anembodiment of the present invention. The x-axis represents the distancefrom the beam center in millimeters. The y-axis represents irradiance inWatts per square centimeter (W/cm²).

As can be observed with reference to the present example, a high densityLED array allows for a wide variety of beam irradiance patterns that canbe projected onto a workpiece, including: high center peak, flat-top tophat and asymmetric top hat.

The present example illustrates profiles for a high irradiance beam 2010at 5 mm stand-off, flat top, top hat beams at 25 mm 2020 and at 50 mm2030 and an asymmetric top hat beam at 25 mm 2040. Asymmetric profilescan be advantageously used in photocuring where oxygen inhibition iscausing tack free cure issues. The entire power portion of theasymmetric beam can pre-cure the top surface of the workpiece polymertack free and also inhibit the diffusion of more oxygen from theatmosphere into the uncured polymer on the workpiece. This graph showsthe asymmetric profile having a higher intensity on the right-hand side,which could be optimal for a conveyor that is running from theright-side of the figure to the left-side. The conveyor could run ineither direction. There could also be dips in the asymmetry or theasymmetric profile could have a higher intensity on the left-hand side.Note also multiple lamps could be arrayed sequentially down the lengthof a conveyor or orthogonal to the length of a conveyor. Each of thelamp head modules may produce different or the same beam profiles (e.g.,high center peak, flat-top top hat and asymmetric top hat).

Integrating the area under the profile curves gives an approximatedegree of the energy in the beam. In a continuous line of reflectors,the 25 mm wide profile 2020 has the same total energy as the 50 mm wideprofile 2030, but the peak intensity of the 50 mm wide beam 2030 isabout one half the peak intensity of the 25 mm wide beam 2020.

A high peak irradiance, nearly Gaussian beam profile can be advantageousfor curing applications that require a lot of energy into a material ona moving conveyor in a short period of time, whereas a top hat profilecan be advantageous for those applications requiring a longer time forenergy input such as those limited by reaction kinetics.

Many photo-chemical reactions have surface curing inhibition relatedaspects that require photons to be injected into the material over along enough period of time for the reaction to take place. If photonsarrive too quickly they may not be utilized as the chemical reactionrequired to get a proper cure takes place in a time period longer thanthe arrival time period of the photons. Thus, it can be advantageous tospread the beam out over a wider area so that the curing material spendsa longer time under the beam without having to slow down the conveyormoving the material under the UV irradiating device. Additionally, thetop hat distribution can provide the required minimum amount of energyfor curing without over irradiating other parts of the material, thuswasting energy. The top hat distribution can be more effectivelyachieved with the high density LED array since the cross section of thelinear (high aspect ratio) radiant area is small, therefore providingbetter optical control. It should be noted that the top hat profiles inthe context of the high density LED array (e.g., LED array 1407) areextremely uniform showing no pixilation or shower head effects of lowerdensity LED arrays.

While embodiments of the invention have been illustrated and described,it will be clear that the invention is not limited to these embodimentsonly. Numerous modifications, changes, variations, substitutions, andequivalents will be apparent to those skilled in the art, withoutdeparting from the spirit and scope of the invention, as described inthe claims.

What is claimed is:
 1. A lamp head module comprising: a power sourcehaving an anode output connection and a cathode output connection; anarray of light emitting devices having a light emitting surface, thearray having high brightness and a high aspect ratio; a submountconfigured to electrically interface with a light emitting device of thearray, the submount including a light emitting device bond pad area andan electrical conductor bond area; a lamp body; a patterned circuit,mounted to the lamp body, the patterned circuit having a high aspectratio in terms of its length and height, the patterned circuit havingformed therein an opening within which the array is located and thesubmount is mounted, and the patterned circuit comprising oppositeelectrical polarity conductive patterned layers including an anode layerand a cathode layer; wherein a first end of the patterned circuitexposes a first portion of the anode layer to form an electricalconnection with the anode output connection of the power source andexposes a first portion of the cathode layer to form an electricalconnection with the cathode output connection of the power source;wherein a second end of the patterned circuit exposes a second portionof the anode layer, which is electrically coupled to the light emittingdevice bond pad area; and wherein the second end of the patternedcircuit exposes a second portion of the cathode layer, which iselectrically coupled to the electrical conductor bond area.
 2. The lamphead module of claim 1, wherein the high aspect ratio comprises a lengthof the array being greater than a width of the array.
 3. The lamp headmodule of claim 1, wherein the patterned circuit wraps around the lampbody such that the first end of the patterned circuit is substantiallyin a plane perpendicular to a plane containing the light emittingsurface of the array and wherein the second end of the patterned circuitis substantially in a plane parallel to the light emitting surface ofthe array.
 4. The lamp head module of claim 1, further comprising acooler assembly having a top surface to which the submount and thesecond end of the patterned circuit are bonded.
 5. The lamp head moduleof claim 1, further comprising a macroreflector, affixed to thepatterned circuit, to direct photons emitted by the array.
 6. The lamphead module of claim 1, wherein at least one of the light emittingdevices comprises a visible light emitting device.
 7. The lamp headmodule of claim 1, wherein at least one of the light emitting devicescomprises an infrared light emitting device.
 8. A lamp head modulecomprising: an array of light emitting devices having a light emittingsurface, the array having high brightness and a high aspect ratio; asubmount configured to electrically interface with a light emittingdevice of the array, the submount including a light emitting device bondpad area and an electrical conductor bond area; a lamp body; a patternedcircuit, mounted to the lamp body, the patterned circuit having a highaspect ratio in terms of its length and height, the patterned circuithaving formed therein an opening within which the array is located andthe submount is mounted, and the patterned circuit comprising aconductive layer and a non-conductive layer; a cooler assembly having aplurality of channels through which coolant flows and having a topsurface to which the submount and the patterned circuit are bonded; ameans for sealing the cooler assembly to the lamp body and forpreventing coolant from by-passing the plurality of channels; and apower source having an anode output connection and a cathode outputconnection; wherein a first end of the patterned circuit exposes a firstportion of the conductive layer to form an electrical connection withthe anode output connection of the power source and exposes a secondportion of the conductive layer to form an electrical connection withthe cathode output connection of the power source; wherein a second endof the patterned circuit exposes a third portion of the conductivelayer, which is electrically coupled to the light emitting device bondpad area; and wherein the second end of the patterned circuit exposes afourth portion of the conductive layer, which is electrically coupled tothe electrical conductor bond area.
 9. The lamp head module of claim 8,wherein the high aspect ratio comprises a length of the array beinggreater than a width of the array.
 10. The lamp head module of claim 8,wherein the cooler assembly comprises a micro-channel cooler.
 11. A lamphead module comprising: an array of light emitting devices having alight emitting surface, the array having high brightness and a highaspect ratio; a submount configured to electrically interface with alight emitting device of the array, the submount including a lightemitting device bond pad area and an electrical conductor bond area; alamp body having an inlet coolant flow channel and an outlet coolantflow channel; a patterned circuit, mounted to the lamp body, thepatterned circuit having a high aspect ratio in terms of its length andheight, the patterned circuit having formed therein an opening withinwhich the array is located and the submount is mounted, and thepatterned circuit comprising a conductive layer and a non-conductivelayer; a cooler assembly having a plurality of channels through whichcoolant flows and having a top surface to which the submount and thepatterned circuit are bonded; wherein the inlet coolant flow channeldirects the coolant toward an underside of the array in a directionsubstantially perpendicular to the light emitting surface; wherein theoutlet coolant flow channel directs the coolant away from the undersideof the array in a direction substantially perpendicular to the lightemitting surface; and wherein waste heat is removed from the array bydirecting the coolant from the inlet coolant flow channel to the outletcoolant flow channel through the cooler assembly; and a power sourcehaving an anode output connection and a cathode output connection;wherein a first end of the patterned circuit exposes a first portion ofthe conductive layer to form an electrical connection with the anodeoutput connection of the power source and exposes a second portion ofthe conductive layer to form an electrical connection with the cathodeoutput connection of the power source; wherein a second end of thepatterned circuit exposes a third portion of the conductive layer, whichis electrically coupled to the light emitting device bond pad area; andwherein the second end of the patterned circuit exposes a fourth portionof the conductive layer, which is electrically coupled to the electricalconductor bond area.
 12. The lamp head module of claim 11, wherein thehigh aspect ratio comprises a length of the array being greater than awidth of the array.
 13. The lamp head module of claim 11, wherein theinlet coolant flow channel and the outlet coolant flow channel areseparated by a divider.
 14. The lamp head module of claim 13, whereinthe divider has a thickness substantially similar to the width of thearray.
 15. The lamp head module of claim 13, wherein the divider has athickness that is thinner than the width of the array.
 16. The lamp headmodule of claim 13, wherein the divider has a thickness that is thickerthan the width of the array.
 17. The lamp head module of claim 13,wherein the thickness is within approximately 10% of the width of thearray.